Feminism/Equality and the changes it has brought.

This isn't a bad thing, which is important to get out early because some far-right groups use it as an example for why we should wind back the clock.

Most women in advanced countries work, they have and want to have meaningful careers. Having children conflicts with that, in the immediate significant time off, and the long term impact of being the default parent when they have issues at school or are sick.

Lifestyles in advanced countries really rely on two incomes. Stopping work for a significant period to raise multiple children is a significant impact on that income, plus the long term expenses of the child combine to reduce that lifestyle. Not having children, or reducing the number, can be an economic choice.

The culture of both parents working also impacts the support network. Your working, your friends are working, the village is behind a desk not supporting you.

Finally women get a choice now, which is a change that is recent, isn't global and doesn't seem to be as widely acknowledged as it should be.

Society needs to change to address these issues and provide these missing supports. Which is going to take time, but as they are addressed we will probably see the birth rates start to climb again.