>Countries that have to pay for healthcare have a strong incentive to keep its population healthy to reduce healthcare costs

It doesn't work that way in practice. It's a weird argument and nobody would ever buy it as there is no obvious cognitive (and politically valid) path from climate change policy to healthcare policy. This is true for America, and Canada and Australia and I suspect every other country.

Also, your underlying assumption, that the American government either has no incentive or is uncaring with respect to keeping the American public health, is just wrong and probably betrays your ideology. Both parties, Dems and GOP, care about people.