Culture is a byproduct of the economy, but the economy itself is a social construct
There aren't many children being born because the economy does not permit it, but this economy was intentionally set up in such a way that made this happen.
The culprit is clearly
industrialism, which among other things renders the distinction between males and females redundant insofar as gender roles are concerned. A washing machine and dishwasher can accomplish a woman's erstwhile gender role of cleaning the house, just as automation can increasingly accomplish a man's gender role of hard labor.
And given that industrial society is here to stay, there can only be an industrial solution to this industrial problem: fertility factories where embryos are cultivated like in Brave New World. But imagine the obvious implications that this will have on the power of those who controls these factories (whether states or corporations)!
This problem is like a mirror image of the Malthusian concern about mass-famine in the early industrial era, which predated the technological solution (pesticides) to the technological problem of apparently unsustainably high birth rates.
The elites have little concern about this stuff (besides some murmuring from Elon Musk), because they have faith in the capacity of technology to resolve all of its own problems, while also expanding their own power in the process!
But what if they're wrong and things go awry?