Because the deeper you get into petraeus, the closer you get to earlier administrations...and betrayal. Do not forget that it was the nsa and state who tried to utterly destroy Bush on Iraq and Iran.
Where did saddam’s weapons go BEFORE our teams had a chance to search for them, and who oversaw that project?
If true, he would be more likely to have become aware of skeletons in the closet once he toke over as DCI. Consequently, the regime would have been much happier to allow him to leave with vague "personal reasons" of an unspecified nature so that they could continue to hold the affair over his head.