The Americans used to personalise their enemies to a childish degree. They aren’t doing it with IS. Obsessing on al-Baghdadi would bring back too much of the Cheney/Blair/Bush rhetoric of twelve years ago and would remind them of the warning they were given that invading Iraq would produce a thousand bin Ladens. Iraq generated al-Baghdadi, the Sunni avenger. It is also because they are no longer much involved.