The original Aphrodite of Knidos has been lost, so we can't say for sure if it was Praxiteles's intention to give Aphrodite a Barbie crotch as a stylistic choice. It may be that he didn't bother because it was under a hand anyway. Or because the sculpture was displayed painted, it's entirely possible that the pudendal cleft was painted on.
There wouldn't have been pubic hair on the sculpture, because the ancient Greeks absolutely hated body hair in art, on all genders.
The Aphrodite of Knidos established the canonical to depict the female form in art. And many European cultures have a major fixation on the ancient Greeks being the pinnacle of art, civilisation and culture, so the influence of Praxiteles has persisted for millennia.