Marriage in the US is in open retreat. As recently as 2000, married 25- to 34-year-olds outnumbered their never-married peers by a margin of 55% to 34%, according to the US Census Bureau. By 2015 those estimates had almost reversed, with never-marrieds outnumbering marrieds by 53% to 40%. Young Americans have quickly become wary of marriage.

Many economists and sociologists argue about different theories, but researcher Mark Regnerus points to what he calls "a more straightforward and primal explanation for the slowed pace toward marriage":

For American men, sex has become rather cheap. As compared to the past, many women today 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.