At some point, would-be parents at the margin decide they don't need a job to attain economic security.
This is basically a way of doing price discovery on the "market rate" of parenthood. Currently we're under-paying and getting the predictable outcome, and we're all out of ideas.
(In fact, I think this should basically be the solution to all labor shortages, of which parenting is just one example. The wage should increase until the market rate is found, even if that wage is much higher than people say it "should be").