Due to the USA free enterprise based health care system, free enterprise and the drive for excellence. The things that have made America great for the last 230 years.

Steady progress …
So tell me why would we want to destroy the best healthcare system in the world, to add a few who are uninsured? Why not just help them buy insurance.
Or better yet, just do a few cost reduction things, like stop the “Edwards ambulance chasers” — Tort reform, loser pays and allow people to buy their own health insurance plans or form their own private co-ops. Government intervention, it all has the same ending, crap for all, except the few who reside in Congress.
CDC report here. Data is only available through 2007.