Instances have to be created and run by somebody, so we automatically have a bunch of admins in the loop.
Then somebody has to make communities on the instances. That involves choosing the purpose of the community, and writing any relevant description or guidelines. So again you inherently start with somebody in charge of the community.
But none of them answer to a corporate overlord. Things are run the way the people decide. And if the people disagree, they can run different communities or instances. There can easily be unmoderated communities, and I’m sure there are.