Not everyone is scared of the Clintons or the govt, not even in the military.
Not everyone stayed in long enough for a pension. Not everyone has a family. Some people have strong consciences. Some people would have been terminally ill with nothing to lose.
Once one person speaks up, others would be emboldened and any pattern of persecution would be confirmation.
And when you bring in other people to convey threats, the circle of knowledge increases. Yeah, you could just have the CO say, your lips are sealed forever, or else, but that probably isn’t enough.
I don't share your blithe dismissals of what the government is capable of. And in any event, they still aren't talking about what they saw, because the cover story has been shown to be impossible: Associated Retired Aviation Professionals Flight 800 Investigation.