That's right, because it always comes into conflict with other priorities, which is natural. It always did. It's just that women couldn't control how many kids they had.
I mean, it's not cultural: it happens across all cultures and religions. Atheists aren't even in the forefront: Czechia and Denmark have relatively decent fertility rates. It's not political: happens both in authoritarian and liberal countries, even worse in authoritarian, both pro-Western (Singapore) and anti-Western (China). Only thing it seems to depend upon, is level of development, the richer the country is/becomes, the lower birthrate is. It's simply that people get the actual ability to choose, nothing else.