Analysis / Dating Catwoman

This trope does have some basis in real life. The idea of the All Girls Want Bad Boys and the Forbidden Fruit tropes play a part.

Because the possibility of a woman being abused is worse than a man being abused

It's quite rare for a female hero to have feelings for, or pursue romance with a male villain, despite things such as the All Girls Want Bad Boys trope. There are several possible reasons why it's often male hero/female villain and not female hero/male villain. In most societies since antiquity, there are various levels of social codes, both spoken and unspoken, that dictate that men should protect women. This could mean that with the hero/villainess dynamic, the hero is there to protect the woman from herself. In a heroine/villain relationship, a woman who would take up the mantle of heroine is unlikely one that would seek (and would be reluctant to accept) protection, not to mention that a villain is unlikely to offer protection. Additionally with a male villain, often he would be a threat, in a way that's indicative of an abusive boyfriend. In the real world, domestic abuse is something both men and women experience, but the socialization around abuse is very different by gender. An abusive boyfriend is worse than an abusive girlfriend thanks to the Double Standard: Abuse, Female on Male.

Because men are easier to seduce than men

There is also the idea that a heroic woman would have the moral fiber to refuse the advances of a villainous man. This carries the Double Standard that a woman can resist her libido if the man is evil, but a man can't deny their libidos even when they should. Some people think that Women Are Wiser, and thus heroines will know to resist the villain's charms and do so. (The existence of the All Girls Want Bad Boys trope proves this isn't universally true.) Some think that men aren't as good as seduction as women. (This stems from the fact that men and women are usually attracted to different things in each other—men are more attracted to physical appearance, which allows for faster seduction.)

Because writers are biased

It could at times be, for example, male writers idealizing their female characters out of Author Appeal, or feminist writers seeking to put out a positive image of women.
http://tvtropes.org/pmwiki/pmwiki.php/Analysis/DatingCatwoman