I find myself disagreeing that the well-worn cliche that 'power corrupts' is the sole reason for this. It's more so that every rung of the ladder is barbed, and a starry-eyed reformist is eager to scale it rung-after-rung so they can finally effect real change, until they finally make it to the top and are faced with the fact that they've been drained dry–a bloodless husk like all the other suits.