China’s emissions per $ of GDP would tend to indicate that their energy infrastructure is inferior and/or their economy is based on a high-energy but lower valued products.
The U.S. has much more capital investment, and relies more on efficiency of production to be competitive. China relies more on cheap labor and has lower capital investments, meaning its factories may be less energy efficient. Less automation, more brute-force methods, more spoilage and waste, etc.
Per capita, America uses more energy because Americans generate much more GDP per capita. No mystery there. This is a pretty bad metric, though. For example, let’s say the entire economy was automated, requiring just one person to push the ‘start’ button. Man, that person’s per-capita energy expenditure is phenomenal!
This is actually a very complex question. For example, if America creates 25% of the world’s wealth, and uses 25% of the world’s energy, is that a bad thing? A lot of the products America makes are exported to other countries, which means the consumption of energy was really the fault of the country that bought the product, but the blame gets put on Americans for having made the product.
Maybe the lesson is that aggregate values like this aren’t of much use, except in the very specific areas in which such statistics are useful measures. And they’re certainly not useful for the purpose of casting moral judgment.