The horny shirtless men are also terrible and I would never want one on my shelf but the cartoon covers 1. Are extremely lazy and boring and 2. Make the books look like they’re intended for a much younger audience than they actually are. The covers appeal to kids and they pick them up pretty often without knowing what’s inside!!
I’m not really sure what you mean. I’m a children’s librarian and I’ve seen plenty of young readers (~9 years old) choose these books because they’re drawn to the covers. And that’s all aside from the fact that it’s a lazy and tired practice. Authors and publishers are perfectly capable of working with artists to design covers that are more visually interesting and better aligned with the content of the book