First, Utters and boobs are the same thing. You’d be better phrasing it like “why don’t cow women have 4 boobs?”. And the answer to that is the same for both; 1) It’s not the artist’s fetish 2) The artist doesn’t feel like drawing it because it’s honestly a pain in the ass 3) dog/cow women, like humans, only have 1-2 offspring so the multiple nipples are unnecessary. 4) It’s not the artist’s fetish.