The government did not realize the historical value of the work, did not have the money to keep the archives well, and ran out of storage space. So, off it went. What was there to hide? Most of it was on TV! I stood behind the ABC lead at the time, Herb Kaplow, as he narrated the live feed for the Glenn launch. "Live" is a misnomer. He was watching a tape delayed by about 30" while watching the scene live, so he appeared to be precognitive with statements like "in about 30" a guard should come out that door" and of course he had already seen that, but it would not air for 30".
The cameras were reduced in weight by having aluminum or magnesium replace parts of the body and mechanism. And these had holes drilled in them to further reduce weight. Red had trouble with the light weight metals deteriorating during testing, so he had to make more than one camera so that one could be worn out during prelaunch tests and the other was "for real". Also, one of the big problems was designing a film advance that fit the thumb on the suit.
The cameras went to the Smithsonian except for a 'blad that was "Lost in Space". There is a story behind Glenn's camera, but that is for another place and another time.