Where is your evidence that the jobs offered to illegals were ever offered or posted for Americans to decide they wanted or didn't want? What is the average time an employer advertized for help before sending a recruiter down to Mexico? What was the pay that was offered to Americans when they turned the jobs down?
The jobs you have to steal or use a forged document to obtain are often jobs Americans would take --- in those cases, often the illegal is pulling a fast one on the employer.
Where is their evidence they weren't?
Guess you think these companies would have prefered to close their doors and go out of business rather than hire Americans?