Medical Doctors are members of a rich and powerful guild. Admission to the guild requires getting into medical schools. That in turn requires entering at least

Medical Doctors are members of a rich and powerful guild. Admission to the guild requires getting into medical schools. That in turn requires entering at least university (really high school) knowing how the pre-med game is played. For this reason, membership in the profession is more hereditary than most and is especially hard to achieve without knowing a doctor through family friends who can talk you through the process. Also, in the USA, churches were historically important social institutions. In a country of powerful religious institutions, members of a powerful guild with significant barriers to entry and therefore strong hereditary lines are often religious. That's not really at all surprising. At least to me.