I have read a few YA books, including ones written by Sherrilyn Kenyon in her Chronicles of Nick series.
For me, I accidentally picked up the book, not realizing it was a YA book because I was going by author only. However, unlike her paranormal romances set in the same world, it's tame and rated for teens, so there's no sex, just young teen romance that goes nowhere really.
I think the Young Adult genre is popular with adult readers because they are quick easy reads but still have story and meaning behind them. Most of them are fun and can be read in a night or two. They aren't complex, which can hold an appeal to a tired reader who doesn't want to be remembering every detail read before as they go towards the end of the book.
