Honestly, it's probably because *most* prologues they've encountered are bad. I think there is something about prologues that attracts aspiring writers like moths to flames--they've read a bunch of books with prologues, and so they put one in their own--but almost every single aspiring novel I've read that opened with a prologue could have been immediately improved simply by cutting it.
That doesn't mean you can't write a great prologue. It just means that it may take more skill than people necessarily realize--and it's entirely possible that the books in the store didn't have prologues when they first came across the editor's desk.
That doesn't mean you can't write a great prologue. It just means that it may take more skill than people necessarily realize--and it's entirely possible that the books in the store didn't have prologues when they first came across the editor's desk.