There's also the fact that what the US is just more important than other countries by virtue of being such a huge chunk of the global economy. What happens in the US has repercussions to people that live in other countries in a way that is much less true of almost every other country in the world.
If the US had a population of 70M and the UK had a population of 340M and the GDPs were reversed - it would be the other way around.