I think your assertion is unfounded and based on your own unreliable assessment.

There is no mystery to the fact the all the wealth is silo'd to a small class of people. Your big assumption is that developed country's are substantially more hospitable to a majority of the population.

When kindness is considered hostility amongst the general population its no wonder why people wont have kids.

The reason I'm thinking of it is I recently read this lemmy thread. The article itself is probably AI and not that convincing but I think people are making some good points about the pressures imposed by expense of housing and how those affect the desirability and difficulty of having children.

Of course a prerequisite for that to matter is that not having children is more of a real choice than it is for people with no resources in a state of poverty. But it isn't necessarily the case that the difficulty of raising children decreases with country-wide affluence, because wealth inequality is a thing, required resources (like housing space) might become more expensive relative to income despite overall increase in income, and other factors like an increasingly atomized career focused society where community can't be relied on as much to help raise children and the expectations placed on parents are higher, maybe requiring high daycare expenses.

So bringing capable workers in means they pay into taxes that support the aging and school-age population, and never had to have their school-age years paid for. They’re a productive member with half the cost over their lifetime.

I agree in principle with the logic here, but if those capable workers are being placed in competition with a population that is financially struggling, and those taxes are not being used to give those people more breathing room, that productivity isn't helping and is being employed on the wrong side of a class struggle.