Or could it be because they have benefited from the system, they think it's a good thing?

For example, I rarely see expats in Asia complain about why there are so many Hollywood movies in Asia.

I would say this also applies to many "non-Chinese" online. They either fall for racist stereotypes, or they have a similar switch in their brain where any mention of China means they are doing something nefarious and evil.

People in China talk about it all the time. But you do have to speak Mandarin or the local dialect to hear it. Many don't want to talk about it in English because it gets annoying to hear expats and tourists preaching to them.

It's all over the literature too. Hell, half of Three Body Problem, the darling of a few years ago, is actually about the Cultural Revolution. No spoilers but suffice to say that the poisoned seeds sown during the ruinous waste of the Cultural Revolution precipitate everything in the story.

This is a good summary, but it's even more nuanced than that.

For example, while China did lose the Sino-Vietnamese War, they did achieve two important objectives.

First, they proved to be a trustworthy ally to Cambodia. This is why those other SEA countries like Cambodia, Laos, and others that were bullied by Vietnam are much more pro-China right now.

Secondly, they showed that while the USSR was a Vietnamese ally, it would not interfere with China.

Isn't that episode the opposite of this? In that episode, it was other people giving you a score, e.g. democracy.

In this case, it's the government giving you a score.