There maybe other reasons, it may have to do with what going on right now. I would have to check what full pardon means, if it means he can still get work in the gov. Considering the DOJ with drew the charges and only a judge didn't follow procedures is may mean he totally cleared.
A judge is not supposed to do prosecutions against a person who no longer has a charge against them. They are supposed to follow the laws and be unbiased, the judge here was not unbiased against this one person.