Imagine a grocery store that works like this:
There are no price tags anywhere. You only find out how much you have to pay when they send you a bill a month later. They can charge any amount they want, and they always charge ludicrous prices because they can. If you don't pay, you can't get any more groceries at that store, your credit rating drops, and you might even be sued. All other grocery stores in the country work the same way.
That's US #HealthCare in a nutshell.