It's not about structured/unstructured play at all. Basketball and hockey teams in the very same USA are world class.
It's about in which sports in the country the pro clubs pay top money. It's that simple. It sets up the incentives for families, and everything else follows.
99.99% of the kids who play in the street have a lot of fun but will never make it anywhere near pro sports.
Basketball is the only sport in the US that has a similar level of hundreds of hours a year of unstructured play, so it makes sense that the US is great at it.
Hockey, who is the US competing against? Canada. No other country in the world takes it particularly seriously, so of course the US is one of the top two countries... (I often tell each of my two kids that they're one of my top two kids.)
It's about in which sports in the country the pro clubs pay top money. It's that simple. It sets up the incentives for families, and everything else follows.
99.99% of the kids who play in the street have a lot of fun but will never make it anywhere near pro sports.