Maybe because they're not trying to make a studio game? The animations are there for people using the sandbox to use, and for any possibilities that they might show up somewhere in story mode either as something the player starts or as one that just happens in the background or without the player's input. You could make the same argument for AAA games that have so many more animations, especially a game like an FPS where you have specific animations for every gun in the game, or adaptive animations that change or add/remove bits of animation based on context.
Besides, I would rather a porn game have a variety of animations, instead of just the same animations that play over and over, like in Illusion games like Koikatsu you only get basic positions with no variations. Also way better than in some games where you can go back to a character to have sex again but only have a single position, like I don't want to do the same reverse cowgirl position with Mrs Archetype Stereotype for the 1000000th time because it's the only sex option.