When their at their job, they can be monitored.
Once they leave their job there is no way to track who they're feeding information to.
The 'courtesy' security clearance needs to end.
They’re not their.
I don’t know how it works but it seems that they could walk in to one of the agencies and get sensitive information, walk out and sell it to the highest bidder.
You have it backwards. The question is "once they leave their jobs" who keeps feeding them information?