I think that there is still an overall hesitancy for many programs to take IMGs. This can be multi-factorial.
First off, there is always the issue with obtaining a visa for many people. I do not know what it takes for a program to be able to accept/sponsor visas, but I think that many times, if programs can fill without having to go through the visa process, they may be more prone to doing so. Especially in this day and age where there are no guarentees with obtaining a visa, and any delay can hinder the applicant's start date and subsequently cause stressors for everyone else in the program.
There can also be questions about the level of training one receives at a foreign medical school. Until a school has produced many rounds of graduates who are out in the world practicing, I think this is a valid worry. Some schools like those in Europe, Australia, and some of the older Caribbean schools have a track record of putting out highly qualified applicants and programs are therefore more likely to take graduates from those schools rather than a relatively young school.
Next, I think there is a stigma against US citizens that go to foreign medical schools. I think that there are some people out there that are under the opinion that it is a last resort for many students, and the reason they are there is they could not get into a US medical school. And, if they were not good enough back then as a student, there are questions as to their abilities now. I know that when I applied, as a US citizen, I applied to over 40 residency programs, and only had 4 interview offers. On one of these interviews I was talking with a US med school student and I know that they had close to 20 interviews with board scores that were nowhere near mine (I know that board scores are only one part of the equation). But, I also know that from what people told me the rest of my application was strong. There was at least one program that rejected me based only on my application being downloaded (they did not even download my letters of rec or my board scores). So, there is a stigma.
And, of course there are the other issues that have been mentioned previously on this post.