I'm not getting your point here, and I don't see what Benghazi has to do with this. At the very least, you are extremely uncreative. People stay silent for many reasons, not just threats. Is it beyond your ability to imagine they were told they were preventing a catastrophe? That they were told a nuke was on the plane, or a biological terrorism threat of some kind, and they had just minutes to act? Cover stories create a DESIRE to remain silent, to regret the loss of life but see it in a bigger context.
Benghazi, on the other hand, was understood by operatives as to its real purpose. So they can only be threatened, not lied to or misdirected.
The game is far deeper than you realize.
After 24 years, at least a few swabbies would be smart enough to realize they'd been lied to.