Of course the fact that the developing countries/ poorer immigrants / poorer past generations / poorer but religious groups within countries / you name it, have higher rates should make this obvious.
I personally don't have kids because for me, they would be a pointless boring chore. But I guess many fellow coastal bubble dwellers cannot admit it and need a cope ;)
An anecdote, someone from Russia asked me how big our house was when we bought it after getting married. Without going into the details, that was the smallest house we were possibly considering for 2 people, I said 1100sqft. They said, oooh, so you are planning to have many children then, with so much space! Nope, we are just spoiled ;)
Thank you. I'm a millionaire. I want kids. I see no near-term path to having them without their costs rivaling that of financing multi-million dollar boats [1].
The fundamental problem is children are extremely expensive, particularly for the ambitious. (I'm putting aside the enormous liabilities that arise from e.g. one's child being disabled or trans or simply rebellious in some parts of the country.)
[1] https://cpag.org.uk/sites/default/files/CPAG%20Cost%20of%20a... page 8
Even at £200k (allowing some inflation since 2012), that's leveled over two decades. Obviously that blossoms then explodes if you fall into the fashion trap of assuming price means quality, particularly for schooling. But these are largely optional costs. Relocating for better state schooling often also grants more affordable housing, at the cost of commuting. If you're already a million up, there are many option.
Even if that is somehow equivalent to your yacht, if that's the springs-to-mind opportunity cost, do you actually want children? Or would you rather have a boat?
It is fairly easy to have a lot of malnourished illiterate children, but people choose to have healthy kids they send to college, which is a lot more time consuming and expensive.