The late, great Roderick Macfarquhar wrote in his Foreword to Wang Youqin's new book Victims of the Cultural Revolution,
...remembrance of things past is...crucial.
But in China, not solely, or even most importantly for the Groundhog Day Effect, for the Cultural Revolution Terror was unleashed by one man and,
The reputation of Mao Zedong...is still too central to the legitimacy of party rule.
The Chinese Communist Party ruled on the CR in 1981. Mao had been under a "misapprehension" as to the true state of the Party and had committed "errors", and then wiped clean the Chinese peoples' remembrance of that terrible past for it threatened the continued "legitimacy of party rule".
In democracies legitimacy is process-determinative and that process is corrective of past errors and defects. But in one-party states the past is a tin can tied to a dog's tail, the state can never outrun it as long as it remains attached. Cutting the can from the tail, erasing memory of it, presents to the future a dog with perhaps an odd, clipped tail, but a dog nonetheless.