Did I miss the part where they discuss the economics of having a larger worker pool? like how that would affect existing workers? that seems like an enormous question to not address fully.
i.e. if you had 5 doctors at 500k, and you opened up, maybe you would have 10 doctors at 300k. This is a natural economic progression. Same with software engineers: open borders would definitely have a stark impact on median income, but there would be more startups and more work and more people employed in the sector.
We require them to go through a US residency.
Something like 1/4 of doctors in the US are foreign born.
http://www.nytimes.com/2010/08/12/health/12chen.html
https://www.theatlantic.com/health/archive/2017/02/the-value...
https://www.forbes.com/sites/nicolefisher/2016/07/12/25-of-d...
Asking an experienced doctor to go through a residency is worse than asking software developers to get a doctorate if they want to write code in the US.
Protection benefits the industry, lack of protectionism benefits everyone else; and patients have much more votes than doctors.
The second part is true, but the patients do not so clearly see the benefit, while the doctors would personally see and feel the pain of such a measure! The interest and understanding of the latter makes them very powerfully motivated.