It's because what he says doesn't make sense. And when reality catches up he moves the target.
Take for example his conversation with Sam Harris[1] where Garry says that Human+Computer will always win over Computer only at chess. If you know about CS, if you've heard about AlphaZero, you can see that even if it might currently be that Human+Computer > Computer it surely won't be for long. It'll come a time that Human will be Computer's handicap, and we might be there already.
Now he moved on to speak about the narrow/general problem, but that doesn't make him any more of an expert.
If you want to listen to an expert look for someone qualified, someone like Eliezer Yudkowsky.
[1] https://samharris.org/podcasts/the-putin-question/