My guessing is because when you get a order to not speak of it and they did, that is the way for them to remove them. Look at area 51 all the people who witnessed what they did alot said , they couldn't talk about it afraid for there jobs and there life, now that was back in the 50's 60's look at Roswell something.
I misunderstood, based on what you said I thought you meant you had personal knowledge of/witnessed careers being ruined. Clearly that's different than what you're "guessing."