I think the government just doesn't find it very interesting. It's like US doesn't really talk super much about MOVE bombings or Kent state massacre. Old history and the current leading guys are so far removed from the leading guys then.
They still ban "people" (I.e. US bots) today if they constantly talk about it, not because it's relevant or sensitive, but because if you saw a lot of foreign adversaries spam the same lines over and over again like a broken record, you'd also just ban them so they're not manipulating the algorithm.
As the algorithims get way more sophisticated with every generation, "censorship" will become less and less noticable, less false alarms, less wrongful bans etc.
It's defintely not anywhere near a top official's pay grade to speak about 1989 June 4. But maybe it's possible for a lower instance, some department with people studying history/political history, with connections to some filmmakers/journalists etc to make a documentry.