I think for many it's a case of "the enemy of my enemy is my friend". USA bad therefore China good.

You also see it when tankies disguss the current Russian war. There's not so much justifying the actual invasion as there is whataboutism about the West.

tankies are anti-west no matter what, so their opinion of things has to be opposite of west/usa

which leads to shit like "west is bad therefore ukraine is bad and russia good"

You're looking for reason and consistency where there is none.

Why do US right wingers who go on and on about "core American values" and the bible cozy up to Nazis and Russia? Obviously those things have literally nothing to do with core American values and the "good old days", in those days large parts of the population took part in WWII killing Nazis and the cold war was still going on. Paying any mind to anything they say is absolutely useless, what they do is what really tells the story. They just want to get their way and the power to punish those who they dislike and those who do things they don't want.

Tankies really aren't any different. They might say they are communists because they eventually want a utopia for all or whatever but what they do is cozy up to hardcore inhumane regimes like China and Russia because it's never been about creating a better world and doing what's right, it's just about furthering and protecting their ideology.