I feel like all life advice in "the middle class" is like... Don't have kids until you have an established career, mortgage, and can afford a babysitter/daycare.

That's not to say the modern situation is entirely caused by that. One thing I thought of is if you're a peasant, kids might not actually be that helpful in the field but you can keep an eye on your kids fucking about while you plow fields or whatever. Once urbanisation and bosses happen, you can't just bring your kid into the office while you make sales calls (unless your child is also losing fingers in the textile factory). Modern farms are also different to older farms; you don't really want your kids to be around heavy machinery too much, though farmers kids I know spent a decent amount of time hanging out with their parents in the combine harvester etc (unlike literally every urban worker I know).

The survey answer of global hopelessness feels a bit post-hoc to me. I know its a popular narrative, but many doomed societies that have felt doomed have had very high birthrates.

Individualism is also another one.