“However, by 1973, the strong preference for families of one or two children became the norm”
That’s because Paul Ehrlich and the Overpopulation hysteria took over the entire country with even Nixon making a big deal out of it and the Rockefeller Commission concluding that “we have no use of further population increase”.
Having 5 kids became an Enviro-crime in the 70s.
They even enshrined this madness in a little decision called Roe v. Wade.
East Asia is not politically correct. The patriarchy rules there. So they should have a high birth rate right? Nope. It's even lower there. We can ignore China because it is communist. Japan. South Korea. Singapore. Thailand.