1. The USA has the best doctors and hospitals. The marginal benefit to having better doctors and hospitals is completely dwarfed by their higher prices. Would you be willing to pay 2x to have a 5% better chance of no complications on a surgery for a rare condition? Well the USA does exactly that.

2. The USA subsidizes drug development for the rest of the world. All the R&D happens here, and the only reason so much money is spent on this R&D is because the drug companies can charge maximum price to Americans. Other countries negotiate as a block to lower prices. This is great for those countries (cheaper drugs) and the drug companies (marginally expanded markets), but it increases the fraction of money from the US going to that R&D.