There are many services which are provided without user fees to Americans, such as police service, fire service, and military protection. No matter how often you need them or if you impose a disproportionate burden on the service system, you still get the service without user fees. The reason for these services being free is that it is generally regarded as being inhumane to force people to come up with the money to pay the police if they are being attacked by criminals or the fire department if their child is stranded on the top floor of a burning building. The same humanitarian concerns apply to healthcare, but the hold of capitalist ideology on the state is too strong to let go of this cash cow, which now makes up 17% of the U.S. economy.
When you consider that Canada covers 100% of its population by spending 10% of its GDP on healthcare while the U.S. covers 80% of its population by spending 17% of its GDP on healthcare, you can see that the private system is also not very economical.