Canada

This is purely speculation on my part, but I think the Canadian Medical Association, the group which represents Canadian physicians, is interested in maintaining a shortage of physicians and, for example, would vehemently oppose graduating 5-10% more physicians starting now as a means of filling the physician gap. Their motivation is to keep existing physicians in very high demand so that they can maximize compensation and job security.

I think the ultimate problem (neoliberalism) is that there are too many people in positions of power that are trying to profiteer off of a system that's intended to provide a public service (e.g., privatization of healthcare, hospital inaccessibility in rural communities, the large number of Canadians without a primary care provider)