Talk to your friends, they might verbally say 'money', but then you see them go on trips and buy food at restaurants. Its much easier socially to say 'money', than 'I don't like/want kids'.
The only reason I have a ton of kids, is because I am planning on setting them up for political purposes as I play Dynasty. Its selfish, and I hope to make lots of money and power from them.
No one else has this mentality. The better question is: "Why does someone want kids?"
Given most people are hedonists(assumed). Would a hedonist want kids? Maybe. They are cute which is dopamine inducing. But less fancy food and lots of crying pains.
Going on trips and eating out are luxuries some can afford because they don't have children...
This is clearly a multifaceted topic.
We got to the point where travel, food, and child rearing were all readily affordable things. Now it is no longer the case.
Our technological ability to travel or produce food has not diminished, indeed these things are cheaper than ever. The cost of child rearing, relative to people's earnings, has gone up.
It would be fascinating to read or perform a study looking at what it would cost to obtain the median material conditions of life from say 1924.
I would expect it would be quite cheap. I imagine a tiny house smaller than modern apartments located in a rural area. There would be no healthcare, cell phone, Electronics, or car.
If these were the expectations, I think it is still very possible to support the family and children on a single income.
Edit: I found this awesome USDA guide from 1934 for how to set up a substance farm on 1 acre.
https://www.nal.usda.gov/exhibits/ipd/small/exhibits/show/su....
Im partial to layout 1, for land north of the Mason-Dixon line, where average quality farmland is about 11k/acre: https://www.nal.usda.gov/exhibits/ipd/small/files/original/5...
Again, you used to be able to have healthcare, and a cellphone, and electronics, and a car, and all these other things (all of which were much more expensive to produce at the time) while simultaneously comfortably raising a family. A nice home in a good area was once a staple of the middle class, not a luxury for the elites.
We didn't sacrifice having children to improve our quality of life elsewhere, technological development has allowed us to keep our material possessions as we get poorer and poorer, while the costs of life that can't be reduced through technology - real estate, education, child care, etc - skyrocket.
Population is a big one that is a pretty big non-starter. Urbanization would be difficult. Housing and zoning codes might be possible. Childcare regulations is possible but unpopular. Lowering taxes to 1994 levels is possible, but unpopular.
There are lots of sentimental reasons a romantic might have kids even if it makes them less happy. In our current culture, sentimental and romantic are synonymous with stupid or foolish.
At the same time, countries tend to get richer when their birth rates fall, as people are spending their time working to produce economic value instead of having kids.
Compare say France, with a fertility rate of 1.82 and a GDP per capita of $43k to South Korea with a fertility rate of 0.88 and a GDP per capita of $42k.
Do not mistake correlation with causation. And do not mistake society getting richer with the individuals in a society having more access to the time and space necessary for raising a family.