Companies want cheap labor, labor locked in with one company, and willing to work 60+ hours a week. Politicians are bought and paid for by business, thus H1-B visas and illegal immigrants are feeding labor pool to increase shareholder value and increase profits. It's not that complicated. If a politician truly cared about America and American workers, there would be no H1-B visas and no illegal immigration for low skilled workers. As a side note, Cezar Chavez was against illegal immigration because he knew that if there was a steady stream of low-skilled farm workers from Mexico, then that would dilute the power of his union. Companies would just hire from the very large pool created by illegal immigration.
It is interesting that this administration had been talking about income inequality, but H1-B visas and illegal immigration lead to more income inequality not less. Again, not too complicated --- low supply higher wages, ample supply of labor lower wages.