> if they arent on birth control they are more likely to engage in behavior that can get them pregnant

Well yes, trivially: it's kinda difficult to engage in behaviour that can get someone on birth control pregnant. The first behaviour pretty much has to be "stop using the birth control".

When I was a teenage boy and learning about periods and the pill for the first time, I thought it obvious that women would choose the pill to stop having periods: they sound awful.

Took a decade or so before I learned that some women actually have much worse experiences on the pill than off. This is presumably why mooncups are really popular. And presumably those also have issues, otherwise I'd have stopped seeing tampons for sale.

I can't tell by your username if you're a woman with the lived experience of what you're stating is the cause of lower birth rates, or one of the many guys like me who just assumed the pill would solve a lot of the problems women talk about?