They didn't decide:
Over at Volokh Conspiracy we read
Did Sampson and Goodling Have Total Control of DOJ Political Hiring?: The National Journal has a fascinating story about the hiring and firing of political appointees at DOJ that may help explain the context of the U.S. Attorney "purge" story:
Attorney General Alberto Gonzales signed a highly confidential order in March 2006 delegating to two of his top aides .... extraordinary authority over the hiring and firing of most non-civil-service employees of the Justice Department. ...Remarkable. And assuming this story checks out, it certainly explains why Gonzales seemed so clueless about the U.S. Attorney firings. It seems that Gonzales had taken himself completely out of the loop of all DOJ political appointee hiring. He had delegated that role completely to two 30-somethings, Kyle Sampson and Monica Goodling; his only role was a formality, required just so that OLC would find the practice constitutional.
Don't kid yourself. These 30-somethings weren't making the decisions; they were merely gears in the machine. They did what their political superiors in the White House wanted (i.e. Rove).
Orin Kerr is such a tool. I believe if you looked up the phrase "useful idiot", you'd see his smiling visage peering back at you.
It doesn't appear that they are too deceptive in covering their tracks. It's almost TOO obvious.
Could it be some kind of Rovian set-up?
Rove, if anything, is more arrogant than smart. Just sayin'.