If you consider starting a family with no hope of ever getting out of renting, as landlords constantly raise monthlies, you might reconsider children.
On top of the issues with people working so often and so hard that they rarely have time to meet anyone outside of work; no wonder people aren't marrying.
Generally the less money you make the more kids you have. It's really a question of prioritization. People say they're holding off on kids for X or Y reason but I think this is more of an expressed vs revealed preferences situation. They would rather chase material wealth for themselves than have kids, and to be clear I'm not judging just observing. Through most of human history mud huts weren't a blocker to having kids.
https://www.statista.com/statistics/241530/birth-rate-by-fam...
Aside from that, it's merely observations/anecdotes, but from what I’ve seen people who have managed to achieve a massive uplift in economic status (say from minimum wage in their mid-20s → net worth north of $500k-$1m in their mid-30s) are more likely to have children than people who’ve always been wealthy. I would theorize that such individuals feel a greater degree of economic freedom, having lived at the bottom and being able to make more effective use of what they have.
A different scenario. It's one thing to function in a world where you have nothing but can always make ends meet because while you aren't earning anything more, at least your expenses aren't increasing. Currently we have a different system.
Previously, but this no longer holds.
https://www.governance.fyi/p/45-why-rising-family-size-tempo...
https://bmcpublichealth.biomedcentral.com/articles/10.1186/s...
https://ifstudies.org/blog/more-money-more-babies-whats-the-...
https://www.demographic-research.org/articles/volume/51/26
https://www.sas.upenn.edu/~jesusfv/Slides_London.pdf
(your paper is five years old, and is lagging broad, rapid global fertility decline trends; it's not income-fertility, its "educated, empowered women with access to birth control have less kids, no kids, and/or delay childbirth" regardless of income, with the caveat being some higher income cohorts and ultra orthodox religions/cultures [Israel] having higher than baseline fertility)
Education and contraceptives as the article I linked are separately correlated and powerful, as is religious adherence. They're all factors. Note that each of these factors is differently important in different countries or regions, so just because you found a study that shows a positive correlation in the Netherlands that it is in isolation important or that it would work the same way in the US.
Even the most generous countries aren’t fully compensating for the costs of raising a family, and the assistance offered by many is less than pocket change. It’s only natural that incentive is going to be low.