The fact that Bethesda's games are full of characters with, to put it mildly, rather funny faces is a bit of a running joke and even in their latest creation Starfield, not all facial animations are perfect. Now we finally have an explanation, or at least a theory by Delaney King who has worked on games such as Dragon Age and God of War. She mentions that various muscles in the face lack contractions, which contributes to the lifeless and fake smile that characters seem to have. She also refers to András Arató (from the meme Hide the Pain Harold) to elaborate on this. In a
thread on X, she goes through this, showing examples with pictures and referring to how, among other things, the orbicularis oculi muscle does not contract as it should, creating the characters' fake smiles.
King goes on to say: "Faces are hard. A bunch of people across several departments have to coordinate and have the money and time to do it right. And the odds of them all knowing both human facial anatomy, expressions and visual communication queues isn't high."