I would argue that many people do “reject” the government, but they do so by abstaining from the political process. This is why participation is low. It’s not a direct threat to the government so the government doesn’t do anything.

The U.S. government is confident enough in their appearance of legitimacy that they allow pretty broad liberty to criticize it. This is in contrast to other governments like China or Russia or even Singapore which are much less secure about their legitimacy.