No disrespect, but historical evidence does not support this argument. I've seen similar claims made in other threads.

Fertility rates have been decreasing (multiple factors) since 1850, even while general prosperity has been increasing. There is a connection between economic uncertainty and marriage/families over the short run. But the most likely causes of declining birth rates are cultural: modernization, freedom, female economic participation, contraception, later marriage or no marriage, etc.

The world has advanced, and the requirement to procreate has diminished. There is lower want/need from eligible individuals.

My parents had no money at all when they married and they were able to scrape together enough to raise three children.