You need to go back a bit further than that. By the 1970s single motherhood was already being incentivized through policy. Once initially for rare hard luck cases, policy went from supporting single mothers to essentially encouraging it. Stigma around it became celebration of it even being considered liberation by many leftist groups. And this is why we have seen such a spread in this type of behavior being taken up by the underclasses across many demographics now. Where as the poor once had very strong families (because they needed each other) that role has been taken up by the state turning mothers into reliable clients and fathers into unaccountable wastes.

As it turns out, The Moynihan Report [1] was 100% accurate and its predictions on where things were going to head have come true.

[1] https://en.wikipedia.org/wiki/The_Negro_Family:_The_Case_For...