

why would any government be okay with people commemorating an attempt to overthrow them?
Because that is free private speech. That is what free speech means.
You are allowed to commemorate Jan 6 in the US. I think you are an idiot if you do so, but that it still your right to free speech.

In this case, I mean that they are not the state. The state itself censors all mentions in their own communications. And the state also censors mentions by people who are not the state, i.e. private persons.