Poorer populations have less access to sex education.
The government pays $850 a fortnight to a single mother, on top of a $5000 baby bonus and various other incentive schemes. Poor social classes see this as an easy means of money compared to working a "dead-end" job.
Maybe they have kids to escape their reality. People cope in different ways; drugs, drinking etc. Maybe they desperately want to live through their kids.
This is likely an accurate thesis based on macro and micro studies.
TLDR Education, empowerment (contraceptives), labor force participation = decline in fertility rate. Provide access to all of the above, fertility rate drops off.
https://ourworldindata.org/fertility-rate#what-explains-the-... (Fertility Rate: What explains the change in the number of children women have?)
Outside of Africa, there are only a handful of countries where the fertility rate is > replacement rate.
https://ourworldindata.org/grapher/children-per-woman-un?tim...