Boy, I puzzled over this one for a long time.
The best answer I came up with was that a good bit of mating behavior is below the surface, and many women don't even realize what they are doing.
Scientifically speaking, women are sexually excited and and drawn to more domineering, powerful, and profligate men, both in relationships and in money. They can't help it without conscious effort and a good bit of training in wisdom. Pheromones, cutural training, and the programming of sexual desire all militate against making a settled, rational, decent choice.
I have found that the older women get, the more they have learned in this regard. After they have been through a few sleazy guys, a few cheaters, etc., they wake up and say: "Wait a minute, I want a guy that treats me decently, even if he doesn't drive a Porche or take me to Hawaii."
Unfortunately for younger men, it's unusual for a woman to do this before 30-35, if she's going to at all.