I'd guess the reason why it's so uncommon as a type of roleplay is because people like being able to connect with characters. We personify them so that they're easier to relate to, and easier to get emotions, ideas, and concepts out of, since emotions and human-like actions and traits are what drive storylines a lot of the time (revenge, love, hate, betrayal, jealousy, the lust for power, greed...etc etc.) Of course, a lot of those are still very possible to accomplish without removing any realism at all, but it feels a lot more limited and difficult, I guess. My character, Lars, wouldn't be the same character anymore just by removing his ability to think and talk like a human would. Personifying it makes it easier to connect and relate to, because we're human.
The idea sounds really interesting, though. I like it ;u;