I'm sure there's more to Sims than being really, really, ridiculously good-looking...

I think our brains are kind of prewired to try and find an aesthetic that pleases us. Plus I think it's easier to make attractive sims since the game mechanic doesn't allow for unmirrored faces (i.e. one side of the face is the mirror image of the other side). So there's no lopsidedness and imperfections in that regard.