It's probably an 80:20 problem of sorts. More like a 99:1. Externally, people mostly appear to be comprised of flesh and hair. Pick any random square inch and the odds are that you will land on flesh or hair. That gets different on eyeballs, but they are still just bags of goo connected to muscle. The devil there is in the details of the blood vessels and the iris and things.

And then you get to teeth, which are like wet rocks. You're building this thing that is going to bomb if it can't do soft, meaty, hairy things convincingly and then there's this itty bitty section you're only going to see sometimes that is a dark membraneous cave full of wet rocks.

I think one thing is they are translucent/subsurface scattering and the enamel->dentin layer shows through underneath in kind of volumetric ways. Even lower teeth will show through behind the tips of upper teeth a bit (with a standard overbite).

I'm not a figure modeller but I heavily use the Genesis 8 digital human from Daz 3D [0]

My guess is that teeth haven't been that interesting to date and that the modellers don't have access to hundreds of reference pictures / geometries of teeth for their modelling. As opposed to reference images of skin textures, etc. Tongues are probably the same. In fact I don't think I have ever created a render of a figure with their tongue out.

Once they take the time, the teeth should be easy to improve.

[0] https://www.daz3d.com/technology/

vfx veteran here

Technically speaking an animator might know. A lighter would have a better idea. And finally a shader writer could tell you exactly.

If you were interested in the more technical breakdown of responsibilities in the industry: (of course it'll change from studio to studio, but this is pretty good)

https://discover.therookies.co/2019/05/22/job-titles-in-3d-a...