Memes

Its commentary on how Margot Robbie's character Barbie contrasts against Barbie the toy whose genitalia is smooth and chaste, signifying how the character is developing into a real woman opposed to an idealized plastic figure of femininity....... Probably.

To confirm we would have to examine the size and presentation of Kens bulge as his character develops. A moose knuckle in the third act would confirm my hypothesis.