You make a good point. Folks like him evidently value power over everything else. They just can’t let go. It ultimately hurts them, and the country.
My working theory is that they are not allowed to retire. It takes time to find somebody prone to being corrupted and there is risk of exposure if the person turns on you. So, if you can find one you would never want to let him go.
A scientist, a performer, a sportscaster calling a game. Those are jobs it makes sense you'd keep doing because there's a challenge and an enjoyment even when you're up there in age. A politician going to a committee hearing? Nah, there's no fun in that. The only conclusion is power and once you conclude that, you shouldn't want that a person who lusts that much for power anywhere near your vote. (And if that disqualified every politician out there, would we bad off?)