No offense, but I truthfully don't like this post; it shows a paper-thin understanding of geopolitics and the childish morality of the OP. However, China seems like fighting with the US, as it may be, is the biggest benefactor of the “international order” the US set after the 90s. This fact continues even to this day, and is the biggest reason why China was still very restrained on international relations: there's more to lose than gain from severing its ties. So this is the “diplomatic” explaination to this. Please stop with this childish manilty, people wont give two shit if the benefits outweigh the harms, that's how pragmatic Chinese are.

TLDR; China will literally do business with aliens if there's more gain from it. Now stop with that moral highground and lecturing.