Independance...

Young Americans have quickly become wary of marriage.  Economists and sociologists argue that this is about men’s low wages.

Another hypothesis blames the decline of marriage on men’s fear of commitment. Maybe they just perceive marriage as a bad deal.  They eventually want to fall in love and have children, when their independence becomes less valuable to them.  

For American men, sex has become rather cheap. Many women expect little in return for sex, in terms of time, attention, commitment or fidelity. Men, in turn, do not feel compelled to supply these goods as they once did. It is the new sexual norm for Americans, men and women alike, of every age.

This transformation was driven by Its widespread adoption of birth control. This  boosted their educational and economic fortunes and reduced their dependence on men. As the risk of pregnancy radically declined, sex shed many of the social and personal costs that once encouraged women to wait.