> If "thinning down the population" was the intent, shouldn't the US reverse their anti-abortion bullshit laws?

There can be more than one motivation, of course.

Also, it's very possible that outlawing abortion can result in a decreased birth rate. E.g., if a woman is scared that she'll have a problematic pregnancy, she may decide to just not have a child instead of risking needing and not being able to get an emergency abortion.