Mexico performs as you'll expect a third world country that loves football to perform, and the US performs as well as you would expect a first world country that is ambivalent to football to perform.
I think the real mystery is, how come Brazil, Argentina and Uruguay play so much better than what you would expect from relatively poor countries?
My guess is that their leagues are fairly developed industries, like you would expect in the first world.
We play football every time in Argentina, not to say in Brazil
Football in Brazil has history, legacy, and mind share. I can name several professional teams from Brazil - Flamenco, Corinthians, Santos, etc. I also know of River Plate, Rosario and Boca Juniors from Argentina. This points to the fact that Brazilian and Argentine teams are older than the Mexican teams.
I cannot name a single Mexican team, and that is partly because the oldest club dates back to the 1940s. The oldest Brazilian and Argentina clubs date back to the 1900s.
> My guess is that their leagues are fairly developed industries, like you would expect in the first world.
Pretty much, like in Europe, if you have any interest/talent in football, you enroll in your local club as a kid and go on from there, in Argentina you have a multitude of leagues until you reach Primera Division, so you have from 5 to 6 levels of competition in between organized directly by the Argentine Football Association, founded in 1891, also ran the first tournament in that same year, which makes it the oldest associated football league other than the British FA cup (1871).
Below that you have the regional/provincial leagues, the least populated province, Tierra del Fuego, has 2; Buenos Aires province has 70+ by itself.