To be honest, I think it's a lot more simple than that. Human writers want to say something because they believe something that matters to them and they want to get it out. AI doesn't believe in anything and it doesn't care about getting anything out. Even when it tries to emulate doing that, it sounds fake.
It's also picked up a lot of habits from the training data, which is heavily weighted toward academia, that isn't written the way normal people write.
I appreciate this article for trying to quantify the strange experience that is reading Claude Code's writing.
The uncanny valley isn't a new concept. It applies across all media an LLM might work in, it's not just about visuals.
To be honest, I think it's a lot more simple than that. Human writers want to say something because they believe something that matters to them and they want to get it out. AI doesn't believe in anything and it doesn't care about getting anything out. Even when it tries to emulate doing that, it sounds fake.