There are a lot of people who can't run a mine or start a new one. There are very few who would chose to work in one. How is it determined who 'must work in one' (coal mine), and who is free to pursue another job like park ranger? I'm also curious what 'must work' entails.
Doctors may like being doctors, but I'm sure there are more who would sign up to be neurologists than gastroenterologists.
Oh, and the doctors take less pay because they like being doctors.