It's really not, at least when you compare OECD countries with one another.

For instance, per capita healthcare spending in the US is 11.4K. The OECD average is around 5.7K

Now, there are a lot of reasons for this gap:

1. Salaries are higher in the US. Health care workers are much better compensated there than, say, in France or Spain.

2. The US has a much lower population density. There are a lot of fixed costs with health care. There are real cost advantages to having a large majority of your population in dense urban areas.

3. The US is first to market/first to adoption for a lot of medical innovation. The R&D costs for anything health care related are enormous. Early adopters bear the brunt of these costs.

4. The US has a hybrid health care model. The two countries that use this model, the US and Switzerland, are one and three respectively for per capita health care spending.