The very good youth development programs with the best resources and coaches are very expensive and price out poorer young players with potential, who also tend to be less white. And on top of that, the coaches tend to be much whiter than would be representative of US soccer playing youth. Think about it in terms of "travel teams" and the like and how expensive it is to actually travel for youth sports, but if you have kids who played hockey or soccer or gymnastics or even swam, you know how important it is to their development to play on a travel team as a kid.
There's actually a similar problem with quarterbacks in football. You pay tons of money and you can get private coaching and high level camps for your kid, and that tends to benefit a wealthier, whiter potential quarterback. Christian Hackenburg is the exemplar here, a kid whose dad paid tens of thousands of dollars to get him private coaching and all this other stuff, enough to put him high above other kids in high school... but eventually the lack of talent catches up. Not soon enough for the Jets, but we can laugh at them.
That's not to say every USMNT player is a Hackenburg, but the youth development system in the US really favors a particular and particularly expensive path of development and makes it much harder for really good but poorer kids to shine, which really hurts poorer second-generation Hispanic kids who are basically born with a soccer ball at their feet. Other countries literally pay the most promising kids to play in their youth systems, almost like juniors in hockey, which is how you get so many working class immigrant kids on the English team for example. But the US also rules that out because paying 16 year olds (or their families) would make them professionals and kill their NCAA eligibility, which is still an important consideration in soccer; though the best American players never play in college, it's not something you can assume unless you're a Pulisic, and a surprising number of USMNT players did play at least a year or two in college.
As for Gonzalez, FIFA allows you to play for any country you have "a clear connection with" which often means parentage (see Tunisia's team being all French-born). Gonzalez isn't even a Mexican citizen. Once you pick a country and play for them at the adult level, you're stuck with them though. But you'll see things like Gonzalez where he played for the US U-17 and U-20 teams and then switched to Mexico despite heavy pleading from the USMNT, but it's not all that common.
