A doctor who was not compassionate, but was good at the job, might have good reason to do it well. Pride in a job well done, competitive spirit, sheer zest for the struggle to bring about a favorable outcome? For the money?
We trust doctors to work with unfailing skill and attention on patients who in no way deserve any compassion. Death row types who were caught in a suicide attempt and will cheat the gallows if they don't pull through, terrorists who have yet to be interrogated, etc. It's a good thing that compassion is not the only motive to good medicine.