Because some girls know that good guys are the very guys who their parents want them to be with, and so they purposefully go for the opposite in order to feel the rush of rebellion. However, this often leads down a sad road of teen pregnancy, drugs, and/or abandonment and heartbreak, and they'll be lucky of the latter is the consequence that they face. Due to that, I actually quite prefer good guys to bad guys. Also good guys aren't assholes.