poor sex ed causes people to not understand how getting pregnant works
I doubt there are many people in the world who know how to have sex that don't also know that sex is how you get pregnant. It's damn near common sense, and it has been since the beginning of recorded history.
You would be surprised. When parents don't want to talk about the subject and people want to force abstinence only education you get people who are only told don't have sex to horny teenagers. In which case they'll engage and not know that pregnancy is an outcome.
Promoting abstinence doesn't mean you go without teaching about pregnancy.
Except that's not what happens in places with poor sex ed. It's a weird subject for people want to talk about and many parents don't like the idea of a stranger teaching their kids this. So they fight the school and you get areas where the school doesn't really teach it and the parents don't talk about it.
Is that way all those awful vintage highschool sex-ed films mostly just disappeared from the late-60s on?