I've lately become a pretty big proponent of gatekeeping. On Reddit I saw a comment that security flaws are simply unavoidable, that they're inevitable because as a web developer they must have 1000 dependencies and cannot verify the security of them all, and that if something goes wrong, there's no way it would be fair to hold them accountable for it. When that kind of mindset has taken root, and it has deeply taken root in the entire Javascript ecosystem, it becomes a real-world security issue that affects millions of people detrimentally. Maybe software development doesn't actually need to be accessible to people who can't write their own IsOdd function.
Another example is that a hobby I loved is now dead to me for lack of gatekeeping; Magic the Gathering. Wizards of the Coast started putting out products that were not for their core playerbase, and when players complained, were told "these products are not for you; but you should accept that because there's no harm in making products for different groups of people". That seems fair enough on its face. Fast forward a couple of years, and Magic's core playerbase has been completely discarded. Now Magic simply whores itself out to third party IPs; this year we'll get or have gotten Final Fantasy, Spiderman, Spongebob Squarepants, and Teenage Mutant Ninja Turtles card sets. They've found it more lucrative in the short-term to tap into the millions of fans of other media franchises while ditching the fanbase that had played Magic for 30 years. "This product is not for you" very rapidly became "this game is not for you", which is pretty unpleasant for people who've been playing it for most or all of their lives.
I played MTG on and off for decades, and the Final Fantasy pre-release was one of the best experiences I’ve had in the community. I met several people who had played MTG and stopped but went back for that set because they loved FF. Plus, it fits. For fans of both franchises, seeing how they ported mechanics was itself part of the fun. Sure, maybe a Spongebob set is weird, but FF felt like a labor of love in many areas.
Also, it became the best selling set of all time even before it was out. Which isn’t an indicator of quality, for sure, but it does show Wizards understands something about their market.
If it were simply that, it would have been fine, sure. I didn't especially hate the LOTR crossover either. There was absolutely room for Magic to have, say, one crossover set a year with a fitting fantasy franchise. I'm not saying a crossover is inherently poison that instantly kills a game. What many established players do hate, and what made me understand the game is not for me anymore, is that they broke their promise for these cards to be segregated from regular play, that they started printing more advertisement crossovers than real cards, that these crossovers became less and less appropriate to a fantasy game setting to the point that said setting is completely gone now, and that they started bastardizing even the regular sets (Edge of Eternities is technically not a crossover, but it does not feel like a real Magic set either and clearly only exists to lay down a gameplay framework for the upcoming Star Trek set).
I'm not sure Wizards does understand their market. As you noted, a set doing numbers pre-release has absolutely nothing to do with its quality; it just means there are a lot of Final Fantasy fans interested in collecting cards. But this is not necessarily sustainable for another 30 years, because those Final Fantasy fans are not necessarily going to stick around for Spiderman, and Spiderman fans are not necessarily going to stick around for Spongebob. The Spiderman set was already such a massive flop that they were trying to identify and blame which content creators/streamers were responsible for negatively influencing public opinion, as though that couldn't have happened organically.
WotC is also just about the most incompetent company in the world when it comes to maintaining customer goodwill lately. D&D 5e still, 10 years on, has no real mechanical depth to character building. There's all the identity politics stuff which is needlessly divisive (such as trying to remove "races" and racial bonuses from new D&D rules because it's not PC). They tried to pull that stunt with the OGL where they tried to alter the deal after the fact because the terms weren't to some bean counter's liking. They sent the fucking Pinkertons to raid a guy's house because he got his hands on a prerelease MTG thing through no shenanigans of his own.
At this point, I'm done with WotC. The Pinkerton thing was by far the worst and what made me turn my back forever. Bad rulesets or design designs with which I disagree are one thing, but I refuse to do business with a company that thinks it's acceptable to use force to try to bully people into sticking to their release schedules. They can pound sand forever.