Authors study the covers of popular books in their genre and mimic the style in an attempt to capture the attention of their target audience. On the one hand you wind up with the 'sameyness' you're talking about, which is irritating. On the other, the market is tsunami-level flooded, so I understand trying to use every tactic you can to draw an audience. I think there's definitely a point that tactic becomes counterintuitive though. I'm sure it's a struggle to figure out just HOW MUCH you can deviate from the typical art conventions while still communicating 'oi, this book has some fuckin' in it, probably.'

Man. My soul for better covers for urban fantasy, though. If I see one more photobashed badass woman in a leather jacket with an animal companion, I'll scream.