[YuukiRey]

I suggest taking a closer look at section 5 ("V. Shifting Priorities and Social Influences"), which starts on page 24 for alternative explanations.

The preceding section does mention studies that show a cause and effect relationship between e.g., income and fertility, but the effect is surprisingly small. The authors conclude the section with:

> “Pro-natal incentives do work: more money does yield more babies… But it takes a lot of money. Truth be told, trying to boost birth rates to replacement rate purely through cash incentives is prohibitively costly.”