"When people suggest that whistleblowers would have come forward, of course, they usually have in mind people who, without being complicit in the operation, came to know about it afterward, perhaps realizing that some order they had carried out played a part in the overall operation. Many such people could be kept silent merely by the order to do so, along with the knowledge that if they disobeyed the order, they would be sent to prison or at least lose their jobs. (see Kevin Ryan as an example of this) For people for whom that would be insufficient intimidation, there can be threats to their families. How many people who have expressed certainty about whistleblowers would, if they or their families or their jobs would be endangered by coming forward with inside information, do so?
RE most of this post TL:DR
Or it could be people who were complicit and regret what they had done as well as those "realizing that some order they had carried out played a part in the overall operation" or those who observed what others had done. Nothing has happened to any of the various truthers and their families except for a few very low profile ones. Nor have AFAIK and whistleblowers or their families died mysterious deaths