Traditional marriage was no bed of roses. Couples married in the first throes of lust, discovered they'd married real people, and, for the most part, made the best of it, getting to know their spouses as human beings rather than plastic figures on top of a wedding cake. It was a matter of commitment, of fulfilling a vow. Sometimes it took a lot of work.
Then came the sexual revolution, with women becoming as sexually active as men, sometimes moreso. And, with sex so easily available, who wanted marriage anymore? After all, there might be someone even better around the corner.
We're gonna end up with a bunch of old people with no partners. Turning forty all alone is no fun.