I guess you have to take what you can get, if it saves face.
If you pull a guy over for stealing a car, and the car turns out to be his own car, you can always bust him for parking too close to the fire hydrant after you pulled him over.
The simpler answer was that when they really looked at Plame and the law, there was nothing there to start with. The idea of it being a High Crime was mostly in the fevered imaginations of the Left, something that many people pointed out, including the person who actually wrote the law on outing agents.
But I suppose they had to nail somebody for something.