1. Natural resources
2. The American dream of entrepreneurship and immigrant success.
3. The work-is-sacred American professional-managerial class.
Stable countries decay due to 3 things. First, import pressure can ruin a nation as all its productivity gets extorted out of it by a pseudo-colonial exporter. Natural resources solve this. Second, general lethargy causes productivity to die. But the secularozed protestant work ethic keeps the gears running. Lastly, productive nations can still lose if they miss technological revolution, which can often happen overnight. But the American dream ensures that no one tries to disrupt like Americans, and the most disruptive foreigners are drawn in such that their aha-moment still occurs here.
It's honestly, perfect.
But, don't let that distract you from freeloaders who ride this wave of American productivity. The housing industry, cartelized middle men, lobbyists & bloated executives might still be net negative.
The US isn't just productive. It is productive beyond the wildest imagination of the rest of world. But, that tends to not show up in the numbers or in practice, because a just as large industry of grifters keeps it from cashing it its productivity.
The US wins, not by being more efficient or effective. But by sheer brute force.