Because this issue is used as a battering ram to weaken the Chinese government. The West keeps talking about there being a 'Tiananmen Massacre' where unarmed students were killed even though behind closed doors US diplomats admit there was no bloodshed on TIananmen. It is really hard to defend yourself against those accusations which are false when the other side doesn't need to produce any evidence whatsoever. What is provable are the deaths of the soldiers and maoists fighting in street battles outside the square but that was not a massacre and funnily enough the West also doesn't like to talk about those deaths