There is a scarcity of the best medical care. The doctor who has pioneered breakthrough treatments is more scarce than the doctor who graduated last in his class.
Is a scarcity of top-level research doctors the reason why insulin is expensive in the USA but not other rich democracies? Similarly, is a scarcity of luxury mansions the reasons why the USA has hundreds of thousands of homeless but not other rich democracies?
No. The reason why insulin is expensive is because the USA has a free market for pharmaceuticals and allows manufacturers to set high prices. The reason why there are hundreds of thousands of homeless is because the USA has a free market for housing and allows homeowners to set high prices.