I get what you are saying about the potential of the YA genre. A good comparison would be zombie movies where under this sub genre we now have funny ones (Zombieland) Romcoms (Warm Bodies) family dramas (Cargo, Maggie) blockbuster action (World War Z) and much more
In theory, there is no reason the YA genre couldn't do the same. Harry Potter, Perks of being a wallflower, and Love Simon were great and got good reviews. Hunger Games got good reviews. I like the Sisterhood of Traveling Pants
I thought the 5th Wave and The book thief were not that good I think they show the potential of YA films to tell diverse stories
But most of them look either generic (Percy Jackson, Divergent, Maze Runner, the upcoming Mortal Engines) or pretty bad, Mortal Instruments, Beautiful Creatures, Twilight
So you can't blame people for seeing the sub genre the way they do.