I'll add that the threat of H1Bs have been used as a threatening tool to US employees by US companies.[0] Can't work longer hours for less pay? Reasonably expect your wages to increase with each year? Fine! We'll hire someone from outside.

And generally, when someone takes a criminally low level of pay for their high skill labor, all workers, domestic and international, suffer.

[0] This is the other side of the coin, career American engineers being fired and "forced"(for their severance) to train cheaper Replacements https://www.nytimes.com/2015/06/04/us/last-task-after-layoff... And Disney is just one example - tons of US companies "clean house" when they get frustrated at a high operating budget.