Because women, whether conscious or not, are attracted to men who act like men. Yet society is telling them that the very men they're attracted to are bad, hence the term "bad boy". More often then not the so-called bad boy isn't a bad man at all, he's a man that acts like a man. He isn't afraid to act masculine, to be protective of his wife/GF, not crying or being on a emotional rollercoaster, has no interest in wanting to explore his inner little girl and to not be a pushover by women.

Yet we're told by society that a man who acts this way is a jerk or a bad boy yet someone who acts like a so-called "nice guy" is nice. Do you know why they're considered nice? Because they're a pushover for women. It's an unconscious way of telling men that if you act masculine it's bad and if you act submissive and feminine it's good.