What a departing employee actually holds
Think about what proximity to a principal teaches over two or three years, with no wrongdoing anywhere. An executive assistant holds the calendar's deep structure: where the principal really is when the calendar says otherwise, which hotel, which restaurant, which gym at which hour. A finance employee has seen the liquidity events, the entities, and roughly what the principal is worth. An IT administrator knows which devices the family uses and how the home network is put together. A driver or office security staffer knows the routes, the residence, and what the protective posture looks like on a normal Tuesday versus a heightened one.
All of it walks out the door at departure, none of it can be deleted, and offboarding as practiced touches none of it. The exposure is not that departed employees become attackers; the overwhelming majority never would. It is that this knowledge now lives outside any duty, system, or relationship the principal controls, subject to the departed employee's future circumstances, grievances, social circle, and susceptibility to elicitation by someone who is hostile.