As a South American myself, I think it's really just far fewer teenage pregnancies and major cultural shifts.

I know the topic of money and affordability always comes up, but in my experience, this holds true even for couples with high income.

I think people just don't see a reason to have kids. They're expensive, a lot of work and get in the way of adult life. In a world where social pressures to procreate are minimal, entertainment and activities are far better without kids, and career driven educated people are the norm, very few people will actively want children. Only those that really see it as a calling in life, probably.

I know me and my wife almost certainly won't have kids, so we're part of this trend.

I think part of it is distortion from women having children later in life - that will represent as a temporary dip in fertility rates. But thats everywhere in the world.