> And a lot did use to be expected. There were social norms to work hard, provide, take care of loved ones, and so on. Today, these norms have largely dissolved. Young men have responded accordingly.

I mostly agree, but I think there are more causes than what is implied by OP.

My suspicion is that working hard is still a social norm, but the way wealth has been distributed over the previous decades no longer lets workers climb the social ladder simply by working hard.

I think birth rates are low because having kids is a luxury, particularly when you have no safety net. Certain low/middle subclasses (for instance, those who inherit several properties) tend to have kids eventually, but they increasingly have them at an advanced age (35+).

Some countries economies -mine, at the very least- have been disfigured to the point where there really isn't a clear motivation to have kids unless you are rich.