This isn't enough of an explanation, because surviving is still harder in such places than it is in wealthy countries with low birth rates. Birth rates are inversely correlated with wealth regardless of housing affordability.
True, I was thinking of colleagues who had moved from Eastern Europe to Ireland and were telling me that it was much more common to have homes without a mortgage, they weren't as likely to be a vehicle for getting rich, NIMBYs weren't such a big thing, etc. Maybe it's a holdover from the Soviet Union.