There used to be an ex-CIA guy who lived in the area where I grew up. Everytime the feds started putting pressure on him about some of his activities, he'd call up a reporter and the local small town paper, and give a carefully nuanced interview, ususally concluding with a statement that he might have some more detail later. The federal investigation would vanish, and he'd drop from sight again.
I don't know if that sheds any light on why the feds won't lean on Wilson. My guess is that his former (or perhaps current) employer is worried about what he might spill.
Good post. There is likely a lot more going on behind the scenes. All I know is...the bad guys like Wilson have to lose here.