H1B visas require you to pay the prevailing wage to candidates. These doctors are not given “cheap salaries.” And they often come with much better practical experience than some American straight out of fellowship.
That’s assuming they’re treated properly and not subjected to unreasonable expectations just because management knows they can hold the worker’s visa over his head.
Not to mention that hiring immigrant workers means lowering the chance of hiring someone with an intimate knowledge of workers rights, making it easier to pull illegal shit without repercussions.
Statistically, it’s much more likely that someone from outside the USA will know and care about worker rights (or even be aware of the concept that voters — or even citizens — can have any rights other than free speech and the right to carry guns) than someone from the USA… most countries have at least some form of workers rights, and some unionisation culture and history, while in the US they’re effectively inexistent…