This doesn’t account for my many peers who studied compsci with access to computers all their lives and suck at it, or some people who I met who never programmed until compsci and were great at it.

Well sure, mere exposure doesn’t create skill. But the point I’m getting at is that without it it’s harder to get good at programming, and it’s likely increased significantly for people in poorer countries over the last couple decades. So some, maybe not all but enough, gained the ability to learn how to code the way westerners of previous generations were able to.