No, "everybody" didn't come through the points of entry. That's a convenient fiction. I was on a rather large ranch in Montana last summer. His Grandpa got a job on a tramp steamer in Ireland, got off in Canada, and walked till he hit east central Montana and met his wife. Then he started ranching and acquiring land. 

And, yes, the whole system is pretty much broken. 

It takes years to get properly approved for a VISA or green card. It also costs thousands of dollars. If gangs in El Salvador are trying to recruit your son you simply don't have that kind of time.