Think about it. You have some sickness with some complication that requires some specialist. Do you want the best in the nation or the best in the world? While the price of flying to Spain for frostbite treatment is probably prohibitive for the best care in the world now, things are changing. With robotic surgeries occurring with the surgeon on one side of the world and the patient on the other it is not long before the best in the world is within reach.
This could be expanded to a bunch of other fields. You are building the largest suspension bridge in the world how about having the best suspension bridge builder in the world build it? In the world of running this is kind of standard. It's great to win a national championship but by far and away being the best in the world is more important. Ask any runner and winning a gold medal at the olympics would be far far better than winning the national championships in the US.
I realize that many fields are hard to quantify and defining one world leader would be difficult. But still, narrowing it down to the best five or ten in the world improves your odds of getting high quality instead of the best five or ten in the US. I also think that the US has many of the world leaders already we just don't advertise that fact. I can guarantee when it comes to space exploration the US has most of the best in the world.
The prevalence of the internet is making it so that companies, almost regardless of the products or services they offer, can be used around the world. While cornering any market is a good thing, cornering the world market is likely more profitable.
Consider your place in the world as you consider your impact. You may be more unique than you realized.