Far be it for me to criticize the truth about crony capitalism and the exploitation of labor but there is another point regarding the type of work many migrants were employed to do.
The farming industry cannot employ just anyone. Most American farmers have been on a tractor from the time they were knee high to a grasshopper and can safely operate the machinery. Can you fill a silo?
Bailing hay (and even something as minor as knowing the difference between hay and straw) is a learned art of farming as well as a grueling time for the farmers to run the machinery that does it, then load it into their barns. It is NOT all strictly physical labor it requires knowledge as well. List every part of the tractor, now tell me what parts need to attach to it to do the aforementioned job.
Safety would be a major concern without the farming knowledge to do a job.
How many know the difference between beef cattle and a milk cow? A jersey vs an angus short horn cross?
How many know that a barb-wire fence cannot be cut during a repair? It will come back to wrap you like a whirl wind fury.
Most Americans unfamiliar with the workings of farm labor would be a major liability on a farm in terms of safety alone, let alone possibly destroying an entire crop. Most Americans unfamiliar with this vocation would not even be able to tell when a field is ripe for harvest, or good soil vs barren.
Some food for thought.