I mean, isn't this what Korean and Japan's policies effectively are as well? Doesn't seem to help much.

Children were not raised in isolation with two parents for most of history, an entire community was looking out for them as well that was incapable of being overwhelmed with that responsibility partially owing to higher child/birth mortality rates. But now we've put the onus of rearing functioning adults on precisely two people whose own personality and parenting traits are widely variable to begin with, if not influenced by the side effects of this two parent only viewpoint themselves.

Government is instead made up of a tiny number of politicians who are even more poorly equipped to make such personal decisions for millions of children.