The Marvel Cinematic Universe, or MCU, when it first appear was a refreshing and interesting. It was exciting to see your favorite comic book characters come to life in the big screen. The X-men were my favorite characters growing up and it was a delight to see them on screen (even if they're not part of the MCU).
The first X-men movie came out more than 22 years ago. The first successful MCU movie (Iron Man) came out more than 14 years ago. Since then, Disney/Marvel have been pumping out Marvel movies like clockwork. I've lost count of how many movies are in the MCU. This is on time of the MCU tv shows they try to push on various networks and streaming platforms.
MCU movies aren't inherently bad or unwatchable. Some are great (Avengers: End Game) and some are terrible (Thor: The Dark World). The problem I have with the MCU is that they've become to predictable and formulaic. MCU movies are the McDonalds of the movie industry. You won't get a great movie, but you know what to expect and get consistency every time you go.
The bigger issue I have with the MCU is that its sucking the life out of other movie genres. The money that would have to gone to making a Western or Rom-Com or Drama movie is now being redirected to MCU movies. The actors and actresses who would have made a great performance in those type of movies are instead drawn into the MCU. For the movie companies that don't own the MCU, they're using their money to try to create their own version of a Cinematic Universe (MonsterVerse, DC Extended Universe, etc).
Continuing with the burger analogy, we're in a world where the only burgers available is at McDonalds, Wendy's, and Burger Kings. Every company who isn't McDonalds, wants to be the next one. Maybe some people want a hole-in-the-wall burger joint instead.
The lack of diversity in movies is driving people into other media (tv, video games, YouTube, etc). Some of those folks might never come back to movies. I find myself watching less movies nowadays than before and more tv shows. Eventually people get tired of the MCU as I have and will want something different. Will they still want to watch movies if these Cinematic Universe are only things available?