We have some Americans with a host of problems. Lack of education, no Father figure, lack of skills, widespread drug use (pot, other), mental health issues, limited family support, unmotivated (normal plus pot effect), anti social, etc. Many have also skipped the trades (skills).
Then we have legal and illegal immigrants who'll take most jobs. They'll cut lawns, dig ditches, wash dishes, work fast food, warehouses, drive trucks, etc. - without an attitude. Many of those individuals work their way up the ladder, start businesses, a food truck, etc. They'll work 5, 6 days without complaining.
Imagine who the employer prefers to hire.