As with everything, the reasons vary. Good and bad.

Curiosity. They're set financially so money isn't a consideration for them at all. Boredom. A means of self sabotage. They believe they have to have a man, even a bad one. They believe they have to stay with a man, even a bad one (religious reasons). He's the exact pilar opposite of the last guy she dated who never prioritized her. He.might be a flake, but he's beneficial in some other way. The sex is really good. He's a cheap babysitter. And so forth and so on.