All human communication is based on simulating the presumed mind on the other end, mostly subconsciously.

When you try that with output from an LLM, it doesn't fit because it doesn't come from a mind. (Or at least not good enough to sustain the illusion.) It's subtly but persistently wrong, and all those little warning flags are tiring.

It's like some absurd event where a plastic animal is put out and real ones try to mate with it, because it meets just enough of the instinctual requirements.