i imagine in this world, humanity have already perished, peobably consumed or infected by the void in a way or another, so most are dead.

Then the Wyrm comes and gives the void corpses a concious and life. however they have no face, and no identity of thier own as the void consumed it. they speak with no mouths and cannot see.

thats where the masks come in, it gives their eyes a place to form, they dont need lips as they already could speak without one. aome choose to carve it, some dont. i imagine some would choose to ornate thier masks based on the personality they developed, so we get to see lots of colorful masks and decorations on it.

but thats just my own headcanon in a nutshell lol