Simple.
These women only see one facet of the guys personality, and buy into it. These guys are charming, misunderstood, brave, abused and the two of them will stand back to back against the world in a noble, courageous struggle. They believe the BS.

These women are needed, and their self-worth is measured by how much they are needed.

There is a certain notoriety and attention in the process, too. They tend to be drama queens.

They also get to be perceived as martyrs, valiant defenders of the oppressed, people carrying hope and inspiration where the world has condemned.

They love it.