Candidate A: Studies 30 hrs a week, no job outside AA school. More time for AA program involvement.
Candidate B: Studies 15 hrs a week, works 15-20 hrs per week in order to stay current with previous profession licenses and whatnot and support family/spouse.
Certainly its possible to work and do well in AA school, but the chances of becoming an exceptional AA increase greatly when you don't have to worry about such things and have more time to invest in your education. Sure some people can even work in medical school, but wouldn't that time be better invested in your studies to give yourself the best chance of matching that lucrative residency?