No American will pick strawberries for $2/hour while a Mexican might. When I had my first calculus encounters there was a Russian guy digging foundation at my friends house. Turned out to be a math professor , but would much rather work in construction because he could make more money for the family. Mind you he was only 300 miles west of his home and making multiple yearly salaries in a month. Guess what, no local guy would dig for the same money, let alone teach you calc on a smoke break.
Why would a large corporation pay more to hire H1B? In any case, some scholars recognize a different advantage of H1B: