If you're spending hundreds of millions of dollars to create and distribute and market films I see why studios would rather invest that money into a sure thing people obviously want to see rather something they're not sure they want to see & could bomb. Eventually people will get sick of superhero movies & there won't be so many. Same with Star Wars movies possibly.
There's still tons of other quality and artistic movies for people to see, it's just that Star Wars and superhero films seem to be dominating the blockbuster genre lately. If it wasn't superheroes it was The Hobbit or Lord of the Rings or Pirates of the Carribean or The Matrix or The Hunger Games etc. They made 8 or 9 Harry Potter movies because people like Harry Potter movies, it's not the end of the world or the death of art. If people want to see superhero movies, leave them alone.