Can you please tell my, as someone who is neither Chinese nor American, "why" I should care if a Chinese company stole from another American company (that in turn stole from everyone) to give me a cheaper service that fits my use case?

The whole AI industry was built upon stealing IP.

The extreme of this is to make IP laws irrelevant and that everything should be in the public domain.

Which maybe is not a bad outcome for humanity as a collective after all.

I don't think that's true. Sometimes the 'why' is lost in time as no one's around to tell it, so we end up with a "if a tree falls in the woods and no one's around to hear it, does it make a sound?" scenario. It doesn't really matter. The thing now exists without a 'why.'