Security clearances are not personal "perks".
A security clearance is basically a set of restrictions placed upon an individual for the convenience of the government. (It allows application of labor and brainpower to tasks that must be kept secure.)
The entire burden of maintaining that security is placed upon the cleared individual -- and responsibility for maintaining that security often burdens the individual far, far beyond the termination of the clearance.
In a properly-functioning security system, security clearances should be (and typically are) terminated when a valid "need to know" (for the convenience of the government) no longer exists. This typically coincides (as did mine) with termination of employment in the cleared job.
Should government need arise, clearances can be reinstated -- if classified knowledge imparted to the individual has been rigorously protected in the mean time.
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IMHO, all government employees' clearances should end with their employment -- and their "exit debriefing" should -- in no uncertain terms -- spell out the legal penalties for breaching the security of their acquired knowledge. And -- in the case of HRC -- those penalties should be applied -- unmercifully!
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Brennan didn't "lose" his security clearance. As a civilian non-employee, he should not have had one!
POTUS: Where's the "blanket" executive order voiding ALL expired clearances?
Clearance is traded as currency within the permanent administrative/consulting state
Not removing clearances when someone leaves office has been a “courtesy” that should never have been allowed.
FOLLOW THE MONEY - EVERY TIME
Try being a government contractor and keeping a clearance for more than 30 days.
Technically and legally, a security clearance is granted to an individual to permit them to have knowledge of certain restricted knowledge and access to and involvement in certain restricted areas of governmental action in exchange for limitations on their individual rights of Free Speech, to limitations on their communicate with certain other persons, restrictions on publishing their writings without permission or editing by government officials, and often their right to travel to certain places in the world without permission.
It will mean that one's life is subject to far more scrutiny by officials than that of an ordinary citizen once one no longer has access to any of the benefits the clearance granted because the specialized knowledge gained cannot be forgotten. The restrictions on the subject are often lifelong even if the benefits are not.