Because why not? AI will simply on average be nicer to talk to than most humans, with clearer thinking and better arguments, less contradictions, and easier to comprehend.
I don't know how humans could compete with that (but it also does not seem all that horrible, given that it will be available to every human.)
This is not to say that this idea is uncomplicated or comfortable, in different ways. Just that I think it's true and that it might even be good.