Out-of-universe, why did the story team decide that everything on Mata Nui, Metru Nui, and everywhere else in the Matoran universe needed to be made of protodermis, when in every practical sense it was the same as normal rock, lava, metal, etc? Wouldn't it have been easier to avoid confusion by not adding that extra layer of complexity? I'm guessing that there was a very specific reason behind the scenes for doing this.
My theory up to now has been this: Since the name implies that protodermis is some sort of "outer skin," this was intended from the early days to be a hidden reference to the fact that the island of Mata Nui and everything beneath it was Mata Nui's body. The fact that it was distinguished from ordinary, inanimate rock was a nod to the fact that it was actually the substance of Mata Nui's living body (or at least its outer layer). Is that about right?