Why do some women break up with their boyfriends once they have something better going for them?

I've known several women who broke up with their boyfriends after their business launched, after their hobby turned into their career, after they started making money doing something they really like/love. Before that, they were living with their boyfriends who were financially supporting them. I try not to judge other people's lives, but these women all had one thing in common even if nothing else: they were all ambitious and opportunistic. They viewed people as opportunities/chances/monetary support before viewing them as friends or lovers. I know that shrewd people like this often get the farthest in life, but at what cost? The cost of having no real human relationships with people? I can't imagine spending years of my life with a man and then dropping him like a hot potato once I no longer needed his monetary support. Maybe if I had it in me I might do it, but I'd make myself sick feeling guilty all of the time.