A lot of people still use Facebook. They will never leave these monopoly platforms until they are destroyed by a worker's state.

How much of said user base is just bots talking to themselves at this point?

Network effect. It's reached a certain size and has a momentum of its own that makes challenging it difficult because everyone else and the answers and answerers are all on reddit not on the alternatives.

It's still usable if you're on old reddit and exclusively stick to subreddits you've joined. For now, anyway