What do you guess is the actual number of illegal aliens in the U.S.? This 12M figure often used has been around since the late 90s. I have to believe it is, at least, twice that number.
Fact is MOST illegals have always been Mexicans.
Sure, there are other folks come here as illegals but they simply don't have the mutual support network the Mexicans do ~ they know this country like the back of their hands.
Note: If you talk to Africans who have watched American and Mexican movies a lot (we are second in line to the Indian movies ~ they have more music) they really can't tell the difference between Americans and Mexicans ~ even think both countries look the same. This is true in much of Asia as well.
Back to the main point ~ because of that mutual support network you find Mexicans coming here to work for a while. They send money back home. Then they leave and somebody else comes up to work and send money back.
It's tough, but for the guys here for the money they put up with privations in the US they wouldn't tolerate in Mexico.
As the man said "It's the money". There is likely more stability in the numbers than most of us realize.