Why doesn't anyone talk about GNW (Gross National Wealth)?

I just noticed a very interesting fact.

GDP of the United States: $18.5B GDP of China:$11.4B

If we look at national wealth...

GNW of the United States: $84.8B GNW of China:$24.1B

The margin of the GNW is 8.5 times higher of that of the GDP! Why is GDP so paraded and why do we never hear about national wealth?