While villagers hold their arms to their chest (effectively making another model element), zombie villagers don't, they have stretched arms that have the texture mapping differently.

The profession textures for zombie villagers has not been changed compared to villagers, making their hand textures not visible at all.

When fixing this, the nitwit's arms should be changed to match the proper torn look as well, as simply remapping them will make it look terrible.

This was the cause for MC-248161. The attached weaponsmith texture is now outdated as the part that was supposed to be on the existing arm elements (but should've been remapped) was deleted.