I don’t know but I would guess: AI is very unrealiable, and can be very fast very expensive.
Some of those options are already possible, though. And not in common use mainly because, well, AI is unrealiable and needs a human watching it.
Answering machine that is following every posts and jump in when triggered by content must be expensive in matter of hardware and pure money. But a model that answer on categorylevel to every topic starters is already possible.
Then there is something like watching IP is quite easy cover without AI but is really problematic. Having same IP is quite common.
Have you checked out Discourse AI and Discourse Chatbot?