When you broke, fukking is your entertainment/hobby.
Well, there's more than that really. Fertility rates have been going down a lot during the last decades, save for Sub-Saharan Africa & some parts of Asia, and those are some of the most underdevelopped countries in the world. Libya, for example, saw its fertility rate go from 8 children/women in 1970 to 2.4 now, below the world's average. Countries like Algeria, Mongolia, Saudi Arabia, Morocco..etc all seen a sharp decline in fertility rates as well. It's just that people overall live better now than they did in the past: higher life expectancy, more access to healthcare, lower deaths from conflicts & illness...
The countries with high fertility rates can be explained with reasons ranging from cultural to economical. African & middle eastern countries (for example) tend to value marriage & family higher than western societies do. It's expected in many of them to marry rather young and have a certain number of children. Also, having more children makes more sense compared to western countries. A poor farmer in Congo will want more children to have a higher chance of one (or some) of them "make it" or have children working/helping early in increasing the family's income. Your average American couple working office jobs doesn't have that need. Also, they have lower access to birth control means or sensibilisation. They have below average life expectancy which forces people to marry/have children at younger age, and higher infant mortality rates (due to poor healthcare or conflicts).
