Maybe the brain is near the mouth as a means to temperature control. If my brain is feeling cold I crave warm tea, maybe not just for my belly but also to rapidly warm my skull goo. If my brain gets too warm I start panting like a beast and slosh my mouth with the cold drink I am having. The upper and lower jaw obviously need skin to avoid dinner time embarrassment but plain old skin has a terrible r-factor. Perhaps my cheeks have adapted to be insulation!
Wow. It’s probably bullshit, but I convinced me about it.