There are a number of theories.
McCain critics believed he was blocking access to non-returned veterans or documents that had comments about his collaboration with the enemy while a POW. I’ve visited the Hanoi Hilton and his jail cell in a Christian mission about 5 years ago now. It was a terrible setting. On the other hand, he did participate in some communist propaganda, I’ve been told. I don’t recall it. The explanation is that torture gets you to do things you don’t agree with. I can see that. I know its true. WaterboardING, for example, does work.
On the other hand, inexplicable types of collaboration DO exist, and the conspiracy theorists said there was that kind of damning evidence against McCain.
McCain’s supporters always stated he did it to protect POW families who didn’t deserve to have old wounds opened up again.
Supposedly he did do a whole lot of talking and not necessarily from being tortured. I’m not going to fault him on that all these years later. But to deny POW families information on their loved ones...to block ANYTHING on the POW’s/MIA makes no sense. He was a POW. He should know what the families went through. If he was not going to be help get any and all information to these families....what was he doing on that committee? The only conclusion I can come up with was to lend credibility to its purpose, which was to shut the door on the information. Why would he do that? What did he get out of it?