like every other civilized people, the Chinese have largely realized that the game is rigged and the only winning move is not to play. the only way to "fix" the birth rate is to reject humanity (education, urbanization, technology) and retvrn to monke (subsistence farming, arranged marriages, illiteracy, superstition), which no civilized country will ever do. even the current TFR of 1.0-1.5 in the civilized world is largely inertial, and it will continue to fall. South Korean 0.7 will seem mind-bogglingly high a hundred years from now,
and 1CP was such a predictably disastrous idea that I seriously doubt the forward-thinking you seem to believe the CCP to posses.
They won't do it willingly. That just means it will happen without their input.
the ideal family has two full-time working parents, paying a mortgage and car loans, consuming as many high-margin domestic products as possible, rearing as many children (future laborers and consumers) as possible, with little to no assistance from the state. and you simply can't have that by force. if you could, you might as well drop the pretense and openly treat your population as slaves.