And really, it's not the actual poor who are delaying having kids into their mid-30s: it's the college educated who make way, way more money than them!
I 100% accept this idea. Most of my ancestors lived the miserable, short lives of impoverished alcoholics. They and their children absolutely experienced trauma from their miserable hunger and disease-ridden lives.
If I can’t see myself giving my child a good life I’m more than happy to wait until I’m able to. Bringing a child into the world isn’t an intrinsic moral good.
For most of the human population, this has genuinely been the case. Most of South/East Asian and African adults are barely 1-2 generations of separation from living in poverty. Most of them are very familiar with the struggle of giving kids a good life in much worse poverty than that experienced in much of the West, and would very much rather their grandkids not go through the same thing.
The even more wealthy one marry and have kids right out of college. Delegate child-caring to grand-parent, and only then start working for their career.
In contrast, you go back 150 years, and class mobility was for the cut-throated, extremely ambitious entrepreneurs. The idea of "get a better paying job working for someone else and fundamentally change my social standing" was laughable. Go back any much further than that, and socioeconomic class was basically immutable.