I think OlympicArmsFan is pretty spot on. I read (past tense) and read (present tense) some in the YA world along the same lines you seem to. I think the books that are decent are pretty obvious and done by real authors - The Twlights, Harry Potters... those books didn't just make a splash, they changed the (YA) culture.
Some people just like to write and target their own audience - young writers or people stuck longing for days gone by. Those can be OK to read if not completely enjoyable. I don't think they're complete money grabbers, just hoping their idea will get picked up by the CW for a YA television show -- The 100, Roswell... but definitely not as polished as full on fiction writers can be, and definitely not as experienced in the ways of the world either which shows when they try to write realistic action sequences or people to people interaction.
Some of the earlier stuff like from the 70's that was written to the YA audience before it was ever officially identified as "Young Adult" was really good - The Myth series is my constant example for this.
Its not rare, but it is special when there are actual story lines, proper grammar, plot twists, character development and rapport, humor and intrigue... all in a YA novel that really holds up. I don't know if its marketing or what since the Twilight books were originally self published, but for whatever reason, a few gain traction and sticking power and a few of them are even decent, most not as much imo.
I know authors are told not to jump genres but seeing as how I'm my own editor, producer and publisher, I'm jumping into YA with a good story as soon as the third book in my original Post-Apocalyptic series is completed. You want to talk about a genre with some good books that you have to wade through a ton of crap to get to, Post-Apoc is way up there on that list.