Three possibilities come to mind:
Is there an evolutionary purpose?
Does it arise as a consequence of our mental activities, a sort of side effect of our thinking?
Is it given a priori (something we have to think in order to think at all)?
EDIT: Thanks for all the responses! Just one thing I saw come up a few times I’d like to address: a lot of people are asking ‘Why assume this?’ The answer is: it’s purely rhetorical! That said, I’m happy with a well thought-out ‘I dispute the premiss’ answer.
Haha “Don’t think about it too hard,” I suggested! But there’s some real value in what you’ve said: I do find your idea of an “audience” very helpful and will have to cogitate on it.
The first thing it makes me think of is a story about Doctor Who that I once made up while trying to sleep: are you familiar with Doctor Who? It’s a sci-fi show like a home-made British Star Trek with more tinfoil and more time travel.
In my story, if you’ll indulge me, one of the characters briefly enters a super-perceptual state where she sees some kind of invisible entity steal the consciousness out of her friend’s head, squirts someone else’s consciousness in there, and then makes off with the one originally belonging to her friend.
It’s like the audience from your analogy walked out of one brain and became the audience for another brain. Her friend wakes up, and doesn’t seem to be any different: the brain his conscientiousness inhabits still has all his memories and nobody else’s, so why would she expect him to be any different? But the “audience” observing their friendship hitherto has been spirited away to who-knows-where and this grieves her.
The middle of the story consists of her trying to track down the entity, and also her trying, with only ambiguous success, to determine any difference in his behaviours or thoughts. She becomes increasingly desperate as she imagines the invisible entity getting further and further away.
In the end, she tracks down a way to re-enter the state in which she perceived the entity originally. This time, she is able to look over a large group of people, and the punch line, of course, is that there are countless such entities swapping our “audiences” from head to head constantly. How many times in the last minute has she herself had her conscientiousness swapped for somebody else’s?
It makes me wonder if the ownership between brain and audience is a thing. Is that connection a necessary thing that is missing from our materialistic definition of a consciousness? Maybe that’s the nagging thing that you call a communication channel.
I’ve got another thought experiment to share which challenges this idea, but I’ve given you far too much to wade through already so I’ll save it.