Why not choose GDP? Or meat consumption? You could choose any pair of correlated variables.

Using “The invention of the single mother” is a poor way of explaining away Bad Marriages and relationships.

Also, there was a UN report which came out that showed that a major factor behind people choosing not to have children, globally, is money.

Money has been shown convincingly to not be an important factor. Please read about it for a while and you will quickly see that it’s a discredited argument, not least because poor people everywhere have always had more children. Also, fertility rates are falling everywhere, especially in countries that are becoming wealthier.