As to people's willingness to move, well, that is clearly a personal topic. I am of the opinion that 4 years is a significant period of life and that it is justifiable to not want to remove your children from their grandparents, or leave your life long home. Now, maybe its because I see young people dying all the time, but 4 years is not an insignificant portion of ones life. I almost didn't go into Rad Onc because of this but ultimately decided it was worth it. Do I have regrets? Sort of. My nieces and nephews are grown, I've missed births, I don't get to go to lunch every week with my brother and Dad, etc. These are real losses, and these are 4 years I won't get back. Now, In my case I had to move for medical school as well so its actually 9 years which makes the sting worse, but the point remains.
For the record, I agree with your conclusion. In fact, I think we need to reduce the number of residency positions back to the level they were at a few years ago. However, if "they" are going to approve expansions, I do think it is helpful to decide whether all new spots are truly equal.