Why aren't the leaders of many Islamic terrorist groups as committed to "martyrdom" as the numerous terrorists

they "employ" for political motives? Just wondering why someone like Osama bin Laden, for example, praises and exalts the "martyrs" he uses, supports, etc., points out how virtuous these "martyrs" are , and points out how they will be rewarded in the next life. If this is the case and they believe such things, why don't more of the actual leaders of Islamic radicalism participate in such "martyrdom" acts instead of sending their followers to sacrifice themselves?