> What are the things that motivates them, and what do they themselves want to do in life?

I suspect quite a few people are looking at the odds of achieving various goals, and simply changing the goals. Such as owning a home in desirable areas, or having kids if you cannot afford a food school district or a job that allows you to be home for dinner.

Or if you have experienced income instability, and you do not feel comfortable bringing children into the world. I probably would not have if I did not find a spouse with income in the top two quintiles. Not that there’s nothing wrong with the alternative, but different people have different risk tolerances and higher (perceived) volatility can be a cause for change in some population wide changed we are seeing.