In "the old" days the Cruise Director used to be responsible for almost all passenger activities, both on board and in port. They used to run the shore excursions as well, until the cruise lines realized how much money they were making on them <G>
In today's cruise world, the job of CD involves a lot of reports and adminstration work, on top of having to present an upbeat and entertaining face for passengers.
I think at the moment there may be a half dozen or so that can handle it all, yet still leave a memorable positive impression on passengers. Not saying others don't do a good job, but they do it managing their staff, as opposed to being the "out front" visible entertainment leader.