>Canada has excellent brain surgeons. The reality is immigration isn't as simple as picking up and wandering across a border. There's nativism, protectionism and of course the ties that keep you bound to your local community. Friends, family, shops, restaurants, a house.
And yet, despite those obstacles, the brain drain is real and ongoing.
In a survey of scientists from 16 countries (<http://spectrum.ieee.org/at-work/tech-careers/the-global-bra...>), the US is the top destination from 13 of the 15 others and the #2 choice from the other two. If you are a Canadian scientist, there is a 16% chance (<https://www.reddit.com/r/dataisbeautiful/comments/37lgxg/the...>) that you will move to the US. That's not "16% of all Canadian scientists that move out of the country move to the US". Let me repeat: *16% of all Canadian scientists move to the US.* They're also likely to be among the top Canadian scientists, too.
By comparison, 5% of all American scientists move to another country, of which 32% go to Canada, so about 1.6-1.7% total. Since the US has nine times more people, that means that in absolute numbers the 1.7% of American scientists is about equal to the 16% of Canadian scientists, but there is no reason to think that the 1.7% makes up the top tier of American scientists; why would the best move north of the border? In other words, the US is receiving the best of Canadian scientists in exchange for an equal number of its non-best. As renewiltord said, "Your brain surgeons will leave and you will be left with the other guy."
>If I told you that I would pay you 30% more to move to Kansas, would you? Why, and why not?
If Kansas paid 30% more for the same job, maybe you and I wouldn't move but a lot more people would move there than the current status quo. But it doesn't.
>Broadly, America has a pretty bad healthcare system, ranked somewhere in the mid-20s globally.
The US does quite well in most patient outcomes. It does not do as well as it could because of the opioid crisis which has singlehandedly reduced average lifespans, and which is more or less independent of access to doctors.
The US's high per-capita healthcare spending is driven to some degree by the very high spending in R&D (the US by itself produces something like 50% of new drugs globally), and is also a function of its much higher per capita GDP, about 20% higher on a PPP basis than Canada and Western Europe outside Norway. (I wish I could find the analysis that discusses this; I'll edit this if I can locate it.)
Regardless, 91% of Americans have health insurance, compared to 95-97% in every other developed country. (There are always people who fall between the cracks, like a Canadian who moves and neglects to update his provincial health care card. The only way to get true 100% coverage is to go the UK NHS route of not requiring a member card at all.) Meanwhile, an amazingly high portion of Canadians don't have a family doctor (<https://www.ctvnews.ca/health/despite-more-doctors-many-cana...>). In Atlantic Canada the shortage is astounding (<https://www.thetelegram.com/in-depth/doctor-shortage/what-we...>). It's one thing to have shortages in rural areas—that happens in the US too—but Halifax?!? I've heard the same occurs in Vancouver too. I can assure you that such a doctor shortage exists nowhere in the US outside really rural areas.
>The vast majority of the healthcare systems ranked higher than America are socialized - somewhere between single payer and two tier. With capped pay. Why aren't all those doctors in America?
If tomorrow the US said that every medical doctor and STEM PhD holder from comparable countries (Canada, Western Europe, Australasia, Japan/Korea/Taiwan) could enter the country with unlimited working privileges, what would happen? To some degree you answered your own question above; of course there would be at least some, perhaps many, that would still not move because of local ties, friends, language issues. But Anglophones, and others who are comfortable with English or want to learn, and don't have such binding ties? Remember, 17% of all Canadian scientists already move to the US.