How is it that Mexico has over 100 million people, is fanatical about soccer and still has always had just an average national team/players? Shouldn't you have been in multiple WC semis and finals by now based on the population size and the love of the game?
To be fair people are not as fanartical as people in Argentina, Brazil, Uruguay wich are the only none first world countries to be succesful (with Uruguay being the huge succes story with how small the country is), in fact Baseball was the most popular sport until TV separated the 2 , baseball being pretty easy for radio play by play plus the influence of USA and Cuba , some say baseball was number 1 until the 60s.
Mexico being in a weak region didnt help , Southamericans had strong tournaments in Libertadores and Copa America to compete for almost 100 years, wich also helped players to be sold outside of their leagues , Concacaf pretty much got proper national teams and club tournaments until the 90s (there were some tournaments before that but no one really cared, even now some Gold cups and concacf tournaments are played with subs and are seen as weak tourneys overall ).
The level of the profesional league is good overall but its not a top league, its also built differentl where Argentinia and Brazil produce tons of young players to sell all over the world, Mexico mostly buyed those players, buying players and Mexican star players not being sold elsewhere truncates younger players.
There are lots of more factors but I guess you can get a Idea why we are pretty much at the level of second tier COMEBOL nations like Colombia, Paraguay ,etc and not Argentina -Brazil.