Because Zero was not trained on human games and Master was? Do we have any model which was trained only from self-play that can beat humans? I don't think so.
> DeepMind didn't find any when training in different ways
Intransitivity may not occur within AG versions but could occur when compared to humans. You need very different types of strategies for intransitivity to occur.
> Are they supposed to run a tournament just to show that a massive improvement that crushes all previous versions can still beat puny humans?
I think so, yes. We do this with Chess. Why should Go be different?
Deepmind is aware of this problem. See gwern's links if you are interested.