1. Because they can. Sex is available outside marriage.
2. Because there's nothing in it for them. More downside risk to marriage than upside potential.
Venker opines about marriage-dodging men:
Perhaps these men know all too well that women initiate the vast majority of divorces — anywhere from 65-90 percent, depending on demographics. And when they do, they take the kids with them and hang hubby out to dry with the help of a court system that’s heavily stacked in their favor.It is a rare guy who hasn't either experienced an ugly divorce or heard a close friend bitterly recount the experience.
