America had the advantage of getting through WW2 relatively unscathed with lots of resources and intact infrastructure that it used to leverage against the reconstruction of Europe, Japan and the USSR and entrench its cultural and economic hegemony. Also the US essentially colonized the West with nuclear weapons under the guise of "Pax Americana" and making the dollar the reserve currency.
That's really it. Not moral superiority, not technical ingenuity, not the indomitable American spirit. Just imperialist opportunism.
Loads of natural resources, no local military threats, and historically a government that stayed out of the way and allowed individuals to reap the rewards of their efforts.
The first is almost impossible to screw up, though we're really trying on the last front.
We're ranked number one based on the summation of all the angsty teen America bad comments on social media. At least that is the stat the press goes off of I believe
