Because while demand for healthcare is inelastic, more healthcare can actually be a bad thing. For example, old people (who are big customers) are often best if they are told to just go home, and look after themselves. Cutting up old people can be a waste of time (since they are unlikely to live a lot longer), and can actually reduce their life expectancy (since they don't always survive surgery).

Also, the money the US spends on healthcare could be better spent educating the people who will otherwise drop out of high school, which drastically reduces their life expectancy (since they can't read so good, have trouble getting jobs which don't involve selling meth, and otherwise have terrible lives).