We don't have a shortage of skilled American labor. And we already bring in 1.1 million legal permanent immigrants a year, 50% of whom lack even a high school diploma. We also import 650,000 temporary workers a year with about two million guest workers being in this country at any one time. If we truly had a shortage of labor, wages would be going up, not down. And we would not be having the lowest labor particapation rates since 1978.
As I tried to explain—many of the low-skill job markets operate within local markets, and thus what you describe is perfectly apt for them.
The higher-skill markets tend not to be localized, and thus don’t follow the rules you outline.