I has to do with the fact that the US Dollar is the de
facto reserve currency of world trade, Wall Street in New York is the largest financial hub in the world (and many of the other major financial centers are in US - friendly nations like the UK as well) and the relative sizes of the economies on each side.
Frankly, as
the reserve currency of the world, it is close to impossible to have inflation.
As
the reserve currency of the world, having a negative interest rates, what a disaster that potentially could be.