Reasons why we'll never see 20+ episode seasons for non-comedy/non-procedural shows anymore, or at least in the near future:
1) Streaming. Because more and more shows are appearing on streaming services, there isn’t as much of a need to reach syndication. So TV shows don’t have a pressing need to reach 100 episodes anymore. That’s why shows are starting to feel like 10-hour movies. Since the production doesn’t have a requirement to make filler episodes anymore, that means they can just focus on making episodes that move the plot along.
As an added point to streaming, since a lot of good shows in the 2010s are serialized (example: Game of Thrones, Stranger Things), they unfortunately set a precedent. Basically, if you want audiences to like your series, you gotta follow the format of other successful shows.
2) A-list movie stars being full-time cast members in shows, as well as the increase in TV special effects. Because of this, budgets for shows have to be carefully monitored, leading to less episodes. Think of it like this; imagine how large the budget of a show starring Robert Downey Jr, Robert Pattinson, and Charlize Theron that ran for 24 episodes would have to be (and the fight scenes in the show would be Hollywood movie level).
3) The audience of today has no tolerance for filler episodes anymore. I think the only space that I’ve seen call for a return to 20+ episodes is Tumblr. Outside of this space, filler episodes have a pretty negative reception (I mean, the term “filler” is already a negative one). Although I can’t say for sure what started this, the three main reasons I usually point to are -
* Anime fanbases making the term “filler” a negative term. As an example, you can find whole guides online for shows like Naruto and One Piece that tells you which episodes to skip since they’re filler.
* Streaming services leading to the rise of binge-watching. Because of binge-watching, audiences are now more used to the idea that every episode matters when it comes to progressing the plot. It’s mainly because you can watch an entire season uninterrupted by breaks, thus a filler episode would stick out due to the lack of plot progression.
* Vine, TikTok, YouTube shorts, and Instagram have led to the rise of instant gratification/shorter attention spans. Honestly, social media in general.
4) Examples of what I mean by present day audiences have no desire to return to the days of 20+ episodes:
* The worst episode of Stranger Things season 2 is usually considered to be Eleven’s standalone episode. It was just ONE STANDALONE episode and audiences lost their mind over it.
* Same with the bank robbery episode in Daredevil Born Again. In fact, that’s why Disney released two episodes that day. They knew that if the only episode they released was the bank robbery episode, there’d be social media backlash (which there was, but it was muted due to the fact that most people focused on the plot-relevant episode anyways)
* The Book of Boba Fett and The Mandalorian season 3 were critically savaged for having too much filler (although the criticism for Mando S3 was justified since wtf was that season)
* As a personal anecdote, the reactors who I follow on YouTube seem very negative to the idea of filler episodes. For example, I watched a stream from BasicallyIDoWrk in which he told his viewers that the right way to watch Ahsoka was to watch the first two episodes and then the finale. So even an 8-episode show like Ahsoka is considered to have too much filler.
To close this off, if you want a real-time example of the death of filler episodes, there’s Agents of SHIELD. AOS was savaged in its first season and one of the main reasons why was because of its monster-of-the-week format. AOS survived because it changed its format into more serialized storytelling. So instead of a season where there’s one overarching plot and several standalone episodes, AOS was basically churning out 2-3 serialized seasons worth of content, but instead of seasons, they were called pods.
