It's a function of the type of applicants that this field selected for over the past 10-15 years. The crowd that applied to radonc (and derm, ortho, etc) tended to be the higher achieving type, who were more likely to come from the same suburbs of Boston/NY/Philly/DC/Chicago/Detroit/Dallas/LA/SF/etc, went to similar colleges, med schools, married similar spouses, etc. Many of them would prefer to live in those same areas as opposed to Salina, KS. Obviously that's not everyone in the field, but I have a feeling it's a good number of them.
The frustration you see on this board is when those attendings realize that moving to those areas may not be possible for them, or may require taking a job where they feel exploited. It leaves a bad taste in your mouth, especially after years of working towards a dream that you find out may not be possible.