People mostly just like to bitch. It's not even like superhero movies are the only thing being made. But they are pretty ubiquitous. I guess people just see so many cross-promoted super-hero movie trailer every time they go see a movie that they get fatigue from the idea of them. Not necessarily the movies themselves.

I was listening to a recent Game Grumps episode where Arin basically went on a tirade about how superhero movies are so bland, and how they don't build the characters and the world... but then turns around and praises some of the more recent movies (Black Panther and GotG I think). It seems people are tired of the hype surround them. Which, honestly, I completely understand.