The movie designs were given human-ish faces to better convey emotion and interact with the human cast on that level.

It's kinda interesting what they are doing with the TF: Prime faces - just using a cut-out sheet for the eyes and mouth shapes. I guess they will use the eye holes to mimic eyebrows and lids to get the characters to emote.

I still don't like how it looks tho. Having the face pinned on like that looks like something out of Silence of the Lambs or Hellraiser.