Here's a theory:
Most of us are at least a little bit lazy (and short sighted). We generally don't work hard unless we have to. Little kids -- who need shoes, and baby food, and pediatrician visits, and Christmas toys, and clothes to replace the ones they've outgrown, and, and, and -- are why we have to. Otherwise, we'd all be beach bums.
A lot of young men have decided they don't want to enter upon such a commitment.
And a lot of young women have concluded it would be foolish to take on that burden alone.
In 50 years, a lot of them will be lonely and uncared for.
In the meantime, the economy will have lost a lot of otherwise committed workers.