I suspect that quite a lot of people get into the movie industry because they want to work on their own ideas. Writing, directing, etc.
But when so much of the industry now revolves around existing IP, they don't actually get to do that. So, they resort to attempting to put their ideas into that IP. Many of them don't fit well.
The fan base wants the existing thing. That's what they're fans of. After getting the existing things, they want things that are at least related, and feel similarly. When one goes to a favorite Italian restaurant, one might branch out and try a new dish, but if you ordered lasagna and get tacos, you're going to be confused....even though tacos by themselves are pretty great.
The corporate system seems to be fixated on advertising what the fans want, but lack a way to actually provide that, overall. Sometimes it works out, but sometimes...it's tacos advertised as lasagna, or worse, tacos stuffed into a lasagna.