In one word: Incentives.
There are many reasons historically, people used to have children and often, many children.
1. Labour - many hands make light work
2. Legacy
3. Old age care plan
4. High testosterone levels
5. Absence of other entertainment/distraction
6. Low infant mortality
1. no longer needed (AI, robots, other basic tech like dishwashers and washing machines)
2. Wonderfully and Sadly with the internet people can leave a permanent mark or stain of themselves on this planet into eternity without having children.
3. The breakdown of the family plus care facilities make this redundant.
4. Need I say more. Easy times + toxic food + sedentary lifestyles drop testosterone levels to a fraction of historical norms.
5. Convenient distractions combined with low testosterone, need I say more.
6. Spares are no longer needed.
I’m sure many other points could be added here but I’m out of time.
Final thoughts, don’t try to convince others to have children. There is a process of natural selection at play here.
There is 1 thing every human on this planet has in common, our ancestors were survivors. This same comment will hold true, thousands of generations from now.