When girls are younger, it's all about the guy who has looks that correspond to the social standard (so currently, being a bit of a pretty boy is always good) and who's popular. That gives them the status they want. If you've pulled a guy like that, you can't be bad yourself...
When you're older, the social status comes more from the job, the money and a physique that offers security rather than style.
That's why you see loads of girls pulling pretty boys when they're young but when you're 30, having a great-looking boyfriend who still cleans dishes doesn't really give you the popularity that it did when you were 16. So they all start going for guys who have a better financial status.