I think there's information asymmetry here. Do you think that many Chinese people know that in nearly all developed countries there's a lot of dissatisfaction and (public) vocal opposition to their own government? It's reasonable to assume that's the fact that China wants to hide from its citizens, because they certainly don't want their citizens to think that they have an ability to do that. Assume all the governments are corrupt and shady and all that, but that's still a stark difference between China and other reasonably developed nations.