How is it not? Or are you saying there is some sort of nationality inferiority that should drive the attainment of non-Americans below that of all others?
Over the past half century, China has brought the most people out of poverty in world history. These are the forces at play.
Inequality within a country is a far greater (inverse) predictor of your unborn grandchild's standard of living than worldwide inequality. There's enough wealth in the world to go around if evenly distributed.
Decreasing inequality between nations is surely a good thing. However, the increasing inequality inside nations is dangerous not just because of a sense of injustice - concentrated wealth implies concentrated power, and concentrated power tends to be at odds with a democratic model.
Also, China may have brought a lot of people out of poverty but they're doing so partially by sacrificing the health and in effect lives of hundred of millions of citizens with pollution way off the safety scale.
Over the past half century, China has brought the most people out of poverty in world history. These are the forces at play.