Because they are the CEOs of this corporation and G.O.D. (guardians of doctrine) they have to be picked very carefully so anyone manifesting the least bit of doubt will never qualify for the job (just look at the Raymond Franz fiasco). So especially ever since his deflection I'm sure every future prospective GB is watched very closely to make doubly sure they are thoroughly under WT mind control.
This of course means scrapping the bottom of the barrel to find such ass holes as evident with this current batch of clowns on the GB and their policies. Which means they are very poor business men and will probably lead the corporation to bankruptcy in the future.