This is for 2 reasons: 1) these are not just China's "backstory" but very much part of its present modus operandi; and 2) China tightly censors the flow of information domestically (GFW, control of all traditional and social media companies, etc.) in order to prevent any public discussion of these atrocities. As such they hardly enter the social consciousness at all or at most in very limited fashion (some offline discussion between close family, friends).

The US has done a lot of fucked up shit (slavery, genocide of Native Americans, just to mention the two most egregious), but at least we can now call out those evils, there can be discussion, calls for reparations, and an awareness so that it never happens again. Germany and Nazism is another good example.