Because it was classified Im sure and I doubt it would be evidence in the form of physical documents it would likely be putting pieces together from people they knew and their own missions.

Think about how many people were involved in Manhattan project and no one knew? Its actually really rare for military to go public because the punishments are insane and I imagine if they don't trust the president they sure don't trust whistle-blower protections. Chelsea manning is one of the few and I have a sneaking suspicion that was an intentional plant by CIA because I see no reason why Obama would pardon It unless it was a reward for something they did.

Also, even if you did go public no one would believe a lot of the stuff anyways so you would be burning your whole life down and quite likely going to jail or getting suicided.