There's no reason to believe they would be "stuck" into perpetuity.

Right now, young people comparatively want fewer kids than the previous generation. That's owing to both life stresses (as they say it) and cultural shift, neither of which are written in stone. The fertility rate has stagnated with prosperity, but the U.S. was also quite developed by the end of the world wars, and we then had the boomers.

> they require a lot of societal wealth

Scandinavian countries aren't particularly wealthy compared to the U.S., Germany, France, Japan and others.