Kate Bolick ponders it:
[N]ow, by choice or by circumstance, more and more of us (women and men), across the economic spectrum, are spending more years of our adult lives unmarried than ever before. The numbers are striking: The Census Bureau has reported that in 2010, the proportion of married households in America dropped to a record low of 48 percent. Fifty percent of the adult population is single (compared with 33 percent in 1950)—and that portion is very likely to keep growing, given the variety of factors that contribute to it. The median age for getting married has been rising, and for those who are affluent and educated, that number climbs even higher. (Indeed, Stephanie Coontz told me that an educated white woman of 40 is more than twice as likely to marry in the next decade as a less educated woman of the same age.)
Rod Dreher, no surprise, uses Bolick's article to argue for "traditional morality":
[Bolick] made a hash of her own marriage prospects because she believed in the emotivist, consumerist idea that maintaining autonomy and maximal choice was critical to the good life. It is inconceivable to many Americans today that true freedom comes through limiting your freedom by committing to a worthwhile discipline, which entails self-giving and self-denial. It is a paradox of life, one recognized by Christianity, that by giving up your life, you gain it — but only, of course, if you give it up for something worth the sacrifice.
Amanda Marcotte finds Bolick's piece lacking for other reasons:
I remain skeptical of the idea that the surge in numbers of single women has anything to do with women's successes and/or men's failures. Bolick interviews one genuine expert in her piece, historian Stephanie Coontz, but neglects to mention Coontz's research showing that educated, successful women are more, not less, likely to be married and stay married. If you stop framing dating as some sort of competition between men and women and instead see it as a collaborative enterprise, another theory for the decline of marriage comes into view: Maybe marriage just isn't working for people anymore. Just because someone isn't married doesn't mean they're alone, after all. Maybe we don't need to come up with replacements for marriage, because it's possible that marriage is declining because people have already started to turn to replacements such as cohabitation, serial monogamy, and having a friend-family instead of a traditional nuclear family.
Chart showing the average marrying ages for men and women over time from NPR.