I'm baffled as to why anyone would want to hire these temporary workers.

The entire point of illegal immigrant labor is that it's cheap *B*E*C*A*U*S*E***I*T*S***I*L*L*E*G*A*L*. If you legalize it, it ain't cheap any more. You've got minimum wage laws, workmen's comp, benefits regulations, etc., etc. to comply with, and all sorts of litigation possibilities (harassment, discrimination, etc.) to hedge against. You might as well hire Americans.

Unless you think that Americans are crappy workers—lazy, shiftless, ignorant, ill-motivated, and unreliable.