Why do women date jerks when there are nice guys available to them?

I have been getting to know "platonically " a guy for six months and he is great to me , but I am not attracted to him the way a relationship should be. I also met this other person a few weeks ago and it has not been as platonic but I am very attracted to him and he is not that great to me.....why can't women be with men that are good to them and always choose the ones that treat them like they are a knotch on a belt?