Blizzard is a private company, it's their tournament, their platform. If they don't want that to be instrumentalized as a political platform then they have every right to disallow that.
For another, very recent, example of this: The International Olympic Committee just issued a strict warning against wearing BLM apparels, or any kind of social protests, at the Tokyo Games [0].
Yet the popular mainstream response to that is not "The IOC is bowing down to attempts of censorship by an evil regime!", as it was the case with Blizzard and China, but all around agreement how the Olympics shouldn't be a political platform.
[0] https://thebridge.in/tokyo-2020/wearing-blm-apparels-social-...