I think Fitzgerald had some personal animus towards Libby. He didn't like the fact that Libby called Mark Rich to congratulate him on his pardon even though Libby was the VP's Chief of Staff. I think it was payback.
Libby was Mark Rich's attorney.
Also, this notion that the administration could have done something is absurd. The justice department, under the leadership of John Ashcroft, was compelled to investigate what could have been a crime ("could have" being the operative term) and Fitzpatrick was appointed the case. That's their job. That's his job. Nothing more, nothing less.
Turns out that thru the course of the investigation it was discovered that there was no outing, but during that investigation, Libby obstructed justice by lying about it. A crime. The end.
Now what in holy hell was Team Bush supposed to do about that in practical terms? Have Fitzpatrick's knees broken? Seriously, what is it you Bush bashers expected here?