This is so common sense. In another world, Spain’s agriculture, Eastern Europeans cause about the same thing as the H1B bad examples you mention. Also in UK’s construction industry or textile manufacturing, same deals.
I have personally witnessed stories of people living in inhumane conditions and being withheld imaginary commissions from their paychecks, having no option to negotiate or walk out of a job, or being fired and sent back to their country with no cash and no possessions.
Free markets and free moving of people is poorly implemented. That is all. Why are we still in Greenspan mode, so many years after he admitted that human greed got beyond his imagination. So, ok, we did it, we ruined the worlds economy out of greed, and yet today we still act as if it doesn’t exist.
As long as expenditures with employees can be “optimized” they will be so. It is a sorry situation … and it could be so easily solved by a clear implementation of work visas similar to the model you described, one must wonder why so much time spent so far waiting on nothing to happen but popular distrust and anxiousness, leading to extremist discourse …