A combinations of reasons. For one the new focus on digital broadcasting meant someone had to front the program. Who if not the governing body? Plus some on the governing body clearly have huge egos, in particular tight pants Tony. Others such as Loesch and Herd seem less eager to be in front of the camera.
But I notice they've cut back severely on their appearances. At first there was a GB member every month, then every second month, then they decided to take December and January off completely. Who knows maybe they'll retreat even further. The one amazing thing about Watchtower cutbacks is they never seem to stop.