In additional to the car dependency (and related issues), the USA still has many immigrants (legal and illegal) from poor countries, who likely have health issues that pre-exist their US residency.
Main headline figure is life expectancy at birth, which doesn’t _really_ account for immigration. In any case, a number of rich countries (Ireland, UK, Canada, the Netherlands, most of the Nordics) have higher immigration rates than the US, so, again, probably not that.