It's just part of the game that authors pick up on the formula of a successful UF - or any other genre. If they can turn their book into something with a twist, something original, along with the copycat portions, and write well, then it becomes a book of its own right. But yeah, I cringe thinking of all the followers that try but never quite pull it off. I'm sure I'll run into a bunch of those as I branch out and read other UF besides DF.
There's nothing new under the sun. Everyone is just re-working what's already out there, so the challenge becomes making it their own, unique storytelling that uses what's been learned and read into a fresh, new perspective. It's not that easy.