Why do bad boys like good girls?

Do they think they will be easy to take advantage of? Or do they think of them as a challenge? Or do they want to take a break from the bad girls and find a girl they can bring home to mom and dad? Because i currently like a "bad boy"- he's actually really sweet, but he has a tough reputation and is a player and hangs out with trouble makers. I'm considered a "good girl" but him and I get along very well and I think he has a thing for me too. But I wonder why me, since he can have any skank he wants, why is he interested in me? I have nothing to offer, or at least nothing to offer a guy whose looking for sex. And he's aware i'm a "good girl", so why does he like me?