You should check the details of what the UPU treaty imposes on the US. I haven't checked, but as they say, it's cheaper to ship from China to US than it is from within the US, and that can't possibly be fair, nor desirable for any reason (including eco-friendliness).
As I understand it this problem isn't unique to the US but all countries and china.
You mean the US should've rather pushed within UPU for fair rules?