Are the penises in Baldur's Gate 3 really too big? They look average-sized to me.

Because it wasn't introduced in American culture as such, it was introduced by a surgeon way back as "a remedy for uncleanliness and deterrent to masturbation in small boys".
Nowadays its just a cultural thing that Americans don't want to acknowledge as unnecessary. This kind of things happens in other cultures as well, even if not circumcision. I recall a debate between an Indian doctor and a female Indian activist because a lot of Indian doctors were still pushing "tightening up veganas via stitching" as medically needed for women's health, and not some weird cultural thing they didn't bother letting go of. Not sure if that's still a thing, that was like a decade ago.

Inconsistent history but most important crux of it is it was catholics that made it so you didn't need to be cut to convert to Christianity.

So when American protestants were going full autismo over the old testament, bringing back israelite shit became popular including getting cut. Muslims also get cut, so it shows that Roman culture was the primary reason it wasn't required in Christianity.

Of course, israelites that came here after world war II also push it the frick out of it but to place the blame solely on them is wrong simply because the practice among baptists to slice off foreskins predates WWII.