On Michael’s point: eppur si muove, I would add a couple of points.
1) Japan, Germany, and Italy had had an experience with democratic parliamentarism. Even Japan, out of the cultural western orbit, had parliament elections and democratic debate, before the military gained full control. Iraq hardly had this kind of experience. 2) The U.S. occupying forces decided to work with officials of the past regime that gave all these countries a sense of continuity in their structure. Abe is Japan’s premier now also because America pardoned his grandfather who might have been some kind of Tareq Aziz. It was like keeping the old guys as drivers while the Americans gave them direction on where to go and how to drive.
In Iraq, America decided to not work with Saddam’s generals and people. Of course it was as if you wanted to drive a car and you don’t have other drivers you put the first comer to the wheel the car will crash. Why did the Americans do that? Possibly three reasons, but I’d be interested in learning more, 1) the U.S. totally didn’t trust the old people (but less than the nazi and the japanese military?) 2) There was a group of exiles boasting to the Americans “we can drive the iraqi car” 3) The Americans were under no pressure to bring Iraq back to shape, like they were with Germany or Japan that had to be re-furbished quickly and re-used in the new confrontation with the USSR.