Doesn't really matter the type of doctor, spending all their time on revenue-generating activities would seem to be better than only 75% generating revenue and 25% on "administrative and bureaucratic tasks" that don't generate revenue and which could be accomplished by a much lower-paid employee ("secretaries and assistants").

Perhaps you're correct that the doctors are simply working much longer hours but that's one group of employees among a hospital's staff who do generally have a lot of power and aren't too easy to make extraordinary demands of.