The last part is only half true, and for completely the opposite reasons to the point they think they are making. Not that in principle it isn't a huge case of this:
Glitch has toxic fans because they cater to a toxic audience. An audience of compulsive and impulsive, emotionally stunted kidults with more parasocial than prosocial relationships. They do this because in that audience there is a lot of money; they spend money on loads and loads of stupid merchandise and if they limit it's production by a definite timeframe? Even more.
Glitch is not an indie production anymore, glitch is not a cozy little art house in Vienna or a group of friends working in their free, Glitch is a freaking LLC (well ltd because UK) that makes money, it has employees who are professionals a lot of the time, it has subdivisions... once you start having to pay company taxes, and market-competitive wages for your employees, and having formal relationships with other companies, you have to keep the ball rolling, you have to keep making money. And if you want to do more stuff than before, for example, working on several in house series at once while also working with other studios on other series while also producing several toy lines of your series, then you have to continuously make more money than before. How long until it has investors and a board?
And if you want to make money, then it doesn't matter how "pure" or whatever your (or your employees') artistic vision is, that takes a backseat to making money, and it always eventually shows when you start making changes to how you interact with your fans, how you modify a story, how you treat your employees.
Gooseworx is a good case of this; they bring her in, pay her to write a show which they market extensively to their target audience, and then leave her to deal with all the public image on her own. Professional studios train their talent on how to deal with fans (or at least, used to) and hire people to manage the entire brand's media presence, which includes mediating and overseeing interactions with fans. But Glitch doesn't do this, even though much of their own talent has worked in these studios and they already have several years of experience. Hell, they probably encourage to some degree the creator talking to fans online because it's good publicity (and bad publicity is good publicity).
The reason GLITCH in particular holds onto their label of "indie", despite their clear cutthroat business model, is because -precisely- the image of an indie studio is far more sanitized among internet audiences, specially the kidults they advertise to. We think of "indie" as being unburdened by quarterly profit reports, as not compromising art for money, as being daring to break new ground and appeal to niche interests instead of mass-marketable ones, as not being mangled by executive meddling. But much of this is not true of many "indie" productions today, and not just in animation. They are all acting like the big mainstream studios and chasing much of the same goals while pretending they are smol uwu beans.
"oh but they release their show for free" ok, so did channel frederator for many years, so does adult swim with many of their shows, so does the MIT with their opencourseware, so do many podcasts in the iHeartRadio umbrella, part of the CC media holdings empire. And "they don't owe you anything" also includes "you don't owe them anything" like brand loyalty; shield them from criticism or blindly consuming their toys and watching their advertisements for those toys.
And indie animators are being "turned away" because they are the same kind of obsessive parasocial kidults who also want to author the big Famous Series (tm) instead of being people with some real vision and meaningful message to send to the world.
The proof is all the indie animators that haven't been turned away. Go on, just open twitter, youtube, e621, bluesky, instagram, you find thousands upon thousands of people making every and exactly anything they want all the fucking time, whether it's trend-chasing "animation meme" slop or a half hour dragons fucking cars porn animation.
birb! studios, tophatbird, atastic, pringusmcdingus, eipril, the succubus tavern guy from china, almost every single webcomic ever... there's always been people online just doing what they want with their means or working off of donations or, for over a decade now, simple paywalls or similar monetization means. But all y'all don't even think of them as "indie" anymore, do you? The image of "indie" has been so warped by these half-corpos that we no longer recognize the baseline and bulk of independent artistry.
You don't want an audience of horrid manchildren? Make something actually deep and meaningful, artistically hones, complex, serious characters and stories, not cartoons for children with mass appeal that viewers are going to pretend they are not for children for no other reason than they say swear words and have middle school-tier sex jokes and fucking "realistic representation of a panic attack"s psychobabble.