Maskchamp.
Good questions. I believe a big part of why the US doesn't have the same problem is that the NRMP governing body is far more diverse than the AFMC and makes more of an effort to govern in the public interest. From the NRMP website, "The NRMP is governed by a Board of Directors that includes medical school deans, program directors, residents and fellows, and non-physician members."
In contrast, the AFMC governing Board is made up of the deans of the 17 Canadian faculties of medicine and a maximum of 4 public members
About - AFMC. No program directors, no residents, no fellows. As an organization, it has no accountability to the public and no public oversight. The AFMC's only responsibility is to its students/graduates. It does not necessarily concern itself with the physician shortage problem other than to advocate for more Canadian medical school seats. IMGs are not really the AFMC's concern.
This is not to say that there aren't biases in the US system against IMGs. US IMGs have only a 60% match rate vs about a 95% match rate for USMGs. The difference is that any biases and barriers in the US tend to be more at the level of the individual residency programs rather than built right into the match policies as in the Canadian Match where there are only about 350 positions dedicated for almost 2,000 IMG applicants, leading to about a 20% IMG Match rate vs 60% in the US.