It's because the prices for everything - drugs, medical procedure fees, administration - are set by the insurance, hospital, and pharmaceutical cartels. Outside of major cities, for instance, hospitals (which are privately owned and run) operate virtual monopolies and can charge whatever they like. Even the ambulances are private firms. The government is (I believe) legally prohibited from negotiating its purchasing prices, and why the healthcare that it subsidises for the elderly and very poor remains so expensive. This is also why, for instance, online pharmaceutical imports from Canada have become so popular, because in Canada, the government actually uses its leverage as purchaser to negotiate a sensible price. It's pretty much exactly what Adam Smith is railing against in Wealth of Nations.
Americans (and increasingly, Brits) are also very unhealthy people by developed world standards. This is probably a big part of why European countries' healthcare systems get much better outcomes for less - their inhabitants are in much better shape to begin with.
Of course, the hospital is the last stop in the line in solving that problem, but it's where most of the political attention gets focused, because you can always just throw more money at it or pretend that Virgin and Carrilion can use their "free-market" voodoo to sort the whole mess. Building a society that isn't riven with chronic social isolation, the exploitation of the vulnerable, the breakdown of community spirit and empathy, and their side effects - obesity, alcoholism, broken families, spiraling incarceration rates, collapsing public services, despair - is beyond what you can envision by looking through neoliberal Overton window.
