Because aggregate statistics completely fail to recognise the massive philosophical differences in the system. It is like saying someone who buys Ferrari is getting ripped off because they aren't choosing to ride a bike.

The US pays more because it provides significantly greater coverage outside of aggregate statistics. All of the innovation in rare diseases is because of the US, in public healthcare systems some diseases are simply not treated because it isn't regarded as economic to do so. How do you even quantify that difference? It is like making a GDP comparison between 1800 and today, what price would someone in 1800 not to die of TB? Life expectancy of 20 years old in many countries? Anyone who compares the two things in terms of cost is a lunatic.

In short though, it is not obvious that a high-cost healthcare system is worse. The US system is inefficient, almost all of this relates to their decision not to use universal healthcare which leads to problems pricing insurance. However, this is not related to the system, there are many countries in Europe and worldwide which have effective private healthcare systems.