This is why H1B needs to be a relatively fast path to citizenship. Without that, the bosses will continue to behave badly.
There's tons of things you can do to make people on visas more empowered to push back at work without them become citizens; and in many cases cutting ties to their original countries.
We should want people who want to stay here long term, because then they have a stake, an incentive to stand up to bosses that want to wreck the place.
As sympathetic as I am to the desires of somebody who wants to come for a while and then leave, I think a better policy would deprioritize such candidates.