The simple answer is that we actually have every major type of health system in the world all at action at the same time in the US. And we let corporations have way too much say in our politics. Hence the mess...
For a good overview of the US health system read "The Healing of America" by T R Reid. Probably the best overview of all major health systems on the planet and most through explanation of why ours is so fucked up.
Sorry for the injection of the 3rd rail.... politics...