I think in large part it may because people don't consciously think about the difference between....
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US government officials or other others deeply embedded in the US power structure criticizing China for its treatment of Uyghurs and the massive amount of propaganda and hypocrisy involved with that.
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The average leftist saying "yah, it seems like from what I can tell China is not treating the Uyghurs humanely" while being under no delusions about both the propaganda and motives involved in most of the information they get and also about the general brutality of the US government.
Coming back at category 2 with "but whattabout the US?" doesn't add anything to the conversation, the vast majority of category 2 agrees with these criticisms of the US.
I think in general, if something is
Then treating it as spam and removing it isn't a bad idea.
When it comes down to it, moderation is always going to be about the grey areas.
That is why it needs to be done by humans and its also why there needs to be many communities with different moderators so that no one moderation policy/team has too much power/cultural blindspots are limited in their impact.
Ultimately I have seen very little evidence that communities don't need strong moderation.