Both of the people mentioned in the links were CIA. One was the former director. Many of the people claiming the Soviet angle are former high ranking officials. They were directly or indirectly fed the Soviet story.
Again, there were probably only a couple dozen people involved in the coup and a couple hundred involved in what they believed to be a good intentioned cover up.
If you were involved in what you believed to be a heroic conspiracy where you believed that you helped saved the world but were sworn to secrecy, would you spill the beans?
There's always squeakers and croakers.