Well, the more you have, you replace “struggle” with fear of loss and paranoia.
You don’t have to work hard in prosperity. You may work but it’s not the same kind of back-breaking struggle labor that you do when you are impoverished.
So now you gain. with that, you fear loss.
People have smaller families because it focuses the prosperity to only a few. This has been encouraged since the 1950s. The US encouraged nuclear families as did the UN — the US because it frankly sold more mortgages and the UN to assist with poverty in India and other nations.
China’s response was extreme with one-child-per-family but it was a similar impetus: reduce family poverty by reducing family sizes, increase mortgages, spread out prosperity at the bottom while increasing it at the top.
China’s plan, while weird was successful and they removed that restriction while removing employee supplied housing in exchange for what became a western style mortgage lending boom… which is now about to implode on them.