In this day and age, people can't afford to just keep having as many children as possible. They stop after two or three because that's really all they can reasonably handle/support. And once a woman goes through menopause, she isn't even physically capable of having children anymore. And most people don't want to have children after a certain age either, because it's too exhausting and there are a lot more health risks for the mother. A woman over 40 is at an increased risk of suffering from complications during the pregnancy/birth, and there is also increased risk of the child being born with disabilities or birth defects. And again, most women start going through menopause when they reach their 50s, making it impossible to have babies anymore.