I went down a Korean rabbit-hole about the Pokémon anime, and came out with this.
Basically, since the Pokeani's indefinite extension in Gen 1 when the property proved far more successful than anyone could have imagined, everything that has gone wrong in the anime can be directly linked to any of the above pictured forces being out of balance.
The Pokémon Company, formed after the Western release of the Gold and Silver games proved beyond doubt that Pokémon was here to stay, is all about the profit motive. They see Pokémon first and foremost as a brand; a lucrative property. They just want the anime to be a vehicle to market the franchise to increase sales; that's it. Otherwise, they don't really care.
Game Freak, the makers of the Pokémon games, are a somewhat different matter. From all I've looked into, they also want the anime as a vehicle to reflect the games, but it's not really about money for them. Some of them even disparage how blatant the Pokémon Company gets with making the anime merchandise-driven. Their interest is primarily in the image of Pokémon, maintaining some level of consistency within the franchise, and ensuring that consumers are generally satisfied and no harm comes to the creative endeavors of their staff.
While on a surface level this is certainly more admirable than the Pokémon Company's base corporatism, what leaks have come out show them taking things way too far, to the point of being just as if not more detrimental. The early production talks about Pokémon Horizons is a good example of this: some of their input is actually well-founded, such as criticizing OLM's apparently typical insistence on leaving certain things vague enough to change based on fan reception rather than have them solidified from the start (in this case, it was whether or not Friede should become a traitor as in Dai Sato's initial story bible), and on some aspects such as Gibeon's motivations and position (how he lived so long, how he operates Exceed, why he's only acting out now, etc.) should be clarified, which they were. But they also showed an unreasonable aversion to some basic plot elements solely because it clashed with their own plans for the games. For instance, Gibeon's Pokémon being a Zygarde had them asking if the show's staff might reconsider, solely because it wouldn't match up with Legends: ZA.
But much worse is this: you know how the "Terrastral Debut" arc was made due to Game Freak complaining that there isn't enough from the Scarlet and Violet games in the story? It turns out, the Pokémon Company secured its creation as part of a quid pro quo exchange, because until OLM agreed to do that arc, Game Freak was refusing to allow Dai Sato and his writing team to use Terapagos, citing how its usage in Horizons (the plot-based ties to Laqua, and being a partner Pokémon to Liko used to reflect her own growth of "coming out of her shell") was at complete odds with Scarlet and Violet's own planned usage of it and would undermine it when they put it into the games. When the anime's staff agreed to do Terrastral Debut, the Pokémon Company overrode Game Freak's ban on Terapagos since if OLM was doing this for Game Freak, then they was now obligated to do something for them in return.
IMO, it's insane - yes, one should want the anime to maintain a general level of faithfulness to the games, but there's gotta be a limit. The games are their own story and the anime is its own story. If the story that Horizon's writers wanted to tell required Terapagos, they should have been allowed to use it with no strings attached. Not liking it being used in a different way as the games doesn't even make sense: Meloetta from the BW anime, "Squishy" from the XY anime, and Poipole from the SM anime are used much differently than in the games, so what makes Terapagos any different? And if you didn't want the anime stealing your thunder in regards to debuting Terapagos, maybe you shouldn't have made it part of a DLC expansion to begin with and had it as a core part of Scarlet and Violet's narrative right from the start!
Then of course there's OLM Studios itself, the makers of the anime. If you think they're completely blameless in all this and at the complete mercy of the Pokémon Company and Game Freak all the time, then get a load of this: people from the Pokémon Company and Game Freak actually wanted to do the sensible thing and retire Ash as the anime's main character for decades. It was OLM's Kunihiko Yuyama, the chief director behind the anime, that refused to let him go and kept him around for so long - not only that, but kept him around in a way that required constant resetting and reinventing, which got the anime's writers so much hate from fans over the years even though there was nothing they could do about it. Only when Daiki Tomiyasu, director of the SM anime, stood his ground against Yuyama and insisted that Ash win the Alola League did the tides turn, leading to it being decided to finally retire Ash at the time of the planning for Journeys' last set of episodes in Summer 2021.
But at the center of this triangle, you have the online fandom. The people who began watching the anime as children and just.....never stopped. Watching the anime and being children, I guess. Going through this rabbit-hole reminded me that I cannot recall a more vile collective of fans outside the Star Wars and Sonic fandoms. Most people, once they grow out of something or no longer like it, just drop it and leave. In fact, that's what happened to most of the anime's viewers during the later days of Johto all through the early days of AG - they stopped watching, while a new generation of kids settled in. All was right with the world.
Except it wasn't, since beyond the intended kid audience was the Periphery Demographic of viewers who didn't quit, who kept watching. And that in of itself would be fine, were these viewers self-aware and understanding that the show isn't made with them in mind, and that it not following the developments they want it to isn't some deliberate slight against them. But in the DP anime, the anime's production team made a grave mistake: they tried to thread the needle and directly appeal to those viewers while also still appealing to the kids. This created a mass psychosis: an expectation that from now on, they will be catered to - Ash will grow more powerful as a trainer and more mature as a person, his past exploits will constantly be referred back to, he will grow up with them. But as said before, Yuyama never had that vision for the character. He was meant to be an eternal 10 year old whom would reset as need be for new audiences of kid viewers. Something that was put into practice with the BW anime.
The online fans lost their minds, and waged a hate campaign against BW and its staff for the duration of its run. Whether it was the Pokémon Company, Game Freak, OLM or all three, someone was spooked by it all, because the XY anime was a "course correction" back to what the fans wanted and then some, complete with Ash looking like a teenager and having a love interest of sorts. The problem? In the process, the anime began hemorrhaging kid viewers! I always knew about the ratings decline, but through this Korean rabbit-hole I learned that Bandai also hosted a regular popularity poll for kids anime. Both DP and BW regularly made it to 2nd or 3rd place. XY? Average anywhere between 6th to 8th place.
Not helping, of course, was that pandering to the online fans didn't work if the anime was still unable to actually deliver on the outcomes they expected. Between Serena not actually getting together with Ash and leaving the show at the end just like past heroines, Ash losing the final round of the Kalos League to Alain, and Ash's super special awesome Ash-Greninja leaving him out of nowhere in the second-to-last episode, the anime's staff was bombarded with hate and even death threats (so much easier than just stopping watching, amirite?)
The SM anime mostly managed to succeed against all odds, not only propelling up to an average of 4th place in the Bandai poll and enjoying incredibly steady viewership ratings of its 3 million-something Japanese audience, but even many of the online fans warmed up to it by the end, especially since, as mentioned before, its director succeeded in pushing for Ash to win the Alola League. But then came Journeys, which surpassed BW in terms of toxic fan hatred. This time the series was trying to appease them too, with so many callbacks and old characters returning, but it didn't matter because the new kid appeal element Goh (and to a lesser extent the casual Pokémon fan surrogate Chloe) was loathed beyond all reason by the fans. That Korean site just details, in paragraph after paragraph, the grievances toward Goh, and I'm sorry, I don't understand how a rational human being can think this way. Not liking him is one thing, but the level of hate for this one cartoon character in a series for children is just insane; from reasons ranging from he's a Mary Sue / Creator's Pet (all for things these same fans would adore if given to Ash) to he's a literal psychopath because he doesn't bond with the majority of the Pokémon he catches (yeah, because they're not his, he is literally an intern who is catching them for a research / environmental preservation facility).
The only difference between this and the BW situation is that Daiki Tomiyasu, now in charge to the whole anime, gave zero fucks, since he knew at this point that these fans weren't the target audience or main source of revenue (which is now not even TV ratings but worldwide streaming, leading to him outright saying "I don't care" when someone pointed out how low Journeys' TV ratings were). In fact, if he had his way, the last episode of Journeys would've been the end of Ash - it was the Pokémon Company and Game Freak, taking advantage of Horizons' pre-production hitting a snag, that got OLM to make To Be a Pokémon Master, since they were legit scared how the online fans would react if Ash was retired too suddenly, outright citing the Ash/Serena shippers' antics and concerns about arson attacks - that's how bad this fandom is! And of course, most fans didn't even like To Be a Pokémon Master either!
Now we're on Horizons, and despite its quality, the dysfunction of the triangle behind the scenes is the same as it ever was. In fact, this third year of the show has been weaker than the previous two, and signs point to the usual suspects being behind it: Game Freak and/or the Pokémon Company with the ham-fisted marketing for stuff like Legends: ZA, OLM with its pacing problems and potential changes based on viewer feedback (according to the Korean site, many in the vocal online fandom who aren't even watching the show in good faith have long assailed Liko as a Mary Sue and overfavored / focused on at Roy's expense, so maybe the sudden sidelining of Liko while increasing Roy's development, plot relevance and achievements is a misguided response), and of course the fandom that continues its hate campaign while crying "bring back Ash!" (so that they can send more hate to the staff based around how they don't use him to their liking!) Its a fucking mess and I hate it so much. -_-
I realize this post is primarily about the unhealthy dynamic between fans and the various entities responsible for the anime (and said entities' dysfunctional relationship with each other), but I'm going to set that aside and respond to some ideas on narrative in here.
(Worth mentioning that I, like many 90s kids, stopped watching the anime in the early Johto years and only caught up with the show when Pokemon GO came along, so take all this for what it's worth:)
When it comes to long-running kids shows, I do think it's possible to reconcile the cyclical nature of the target audience with older viewers and the desire for some measure of growth and continuity. Indeed, I would say the Pokemon anime did a fairly good job through DP at it. The show is, by nature, largely episodic, so it's not that difficult for new fans to come aboard. Serialized elements are loose, but still cohesive (abandoned GS Ball plots aside...) Ash's circle of close friends was still narrow enough in those days that cameos and extended guest star runs were manageable, and Ash himself evolved as a character (by accident or design) into a more mature, capable Trainer than he was in the early OS, with the stats to prove it. His playing the role of more experienced friend/mentor to May, Max, and Dawn (to varying degrees) brought something new out of his character, as did his rivalry with Paul compared to his rivalry with Gary. And I would say that it's easy to underestimate both kids' ability to pick up on continuity and the appeal of finding new things in a series once you can re-watch it beginning to end.
I would also say that, by the end of DP, Ash had developed as much as you could reasonably expect him to in an episodic show meant for kids. The long-time members of his supporting cast (Brock and the TRio specifically) were tapped out well before then, and the insistence on rotating out Pokegirls meant that those major supporting characters who still had somewhere to go in their development weren't going to get the chance. Changing that, and shifting to a more serialized show where Ash matured along with a segment of the audience would have been a fundamental alteration, and continuing on with the status quo - the route they took - was always going to be uneven.
In hindsight, the best narrative compromise would probably have been to retire Ash at the end of DP but have him be a semi-regular guest star for short story arcs - a more carefree, lighthearted Tommy Oliver type who would be the connecting glue between otherwise distinct entries in a now-anthology series. But, circling back to the point of the OP, I'm sure that would have spawned its own intense fan reaction.
