Fan Anger and Entitlement.
One of the biggest problems with modern fandom is that many fans cannot make the distinction between "This is not the direction that I would have taken if I were making this" and "This is bad".
Likewise, I think many of those fans have difficulty differentiating between "Respect for the original creators' vision" and "Respect for my interpretation of the creator' vision".
Another one that comes up a lot is differentiating between "This is awful" and "I am not the target audience for this".
Many years ago, some friends of mine used to host viewings of Doctor Who and a lot of the episodes used to rub me the wrong way. Occasionally, I'd get pissy about that, and they were kind (and patient) enough to point out that first point: "Just because it's not the same as the version you've got in your head doesn't make it bad."
In fact, sometimes, it can make it better, by doing something that's surprising, or by presenting a new twist or perspective you hadn't considered before (which is one of the main functions of any kind of art).
I'm grateful for that revelation as it's helped me greatly in being aware of my own reactions to things. It means that I spend more time enjoying things and less time making myself angry about stuff that doesn't really matter.
If I don't like 'My Little Pony', for example, that's entirely reasonable. I'm a dude who's approaching 50. But I can see that it's a well-written and produced show, and I'm glad that shows like it exist for its intended audience.
Plus, to be fair, between movies and TV and comics and games and novels and all the various streaming services and whatnot, there is SO MUCH STUFF out there.
If there's something I don't like, it's not like I don't have a near limitless choice of other things I can enjoy, plus, Holy Shit! How much old and archival stuff is out there? If I absolutely MUST watch Doctor Who and don't like the new stuff, I have twenty plus years of old stuff to watch, and if I run out of that, there's still 'Sapphire & Steel' and 'Tomorrow People' and 'Quatermass' and all that other cool stuff from the time which was riffing on similar material, and almost all of it is more readily available than EVER before!
Make no mistake, there is still genuinely shitty stuff out there, but there's also a lot of misplaced anger about stuff that's perfectly fine - it's just not FOR you.