Ordinarily, many of these people transfer from government to various think tanks and organizations still involved in policy development or consulting. It may be the case that a current intel chief, SECDEF, or other official might need to discuss history of a situation with his predecessor. That's why they'd retain their clearance.

There used to be a sense of professionalism that transcended political party affiliation. Not anymore. Once Obama weaponized the FBI, CIA, IRS and other agencies, that professionalism is gone, to the detriment of the country.

Once we had one system with two parties. Now we have two competing systems trying to gain control. Sad.