I've heard more than a few interviews with David Paulides and his research is very interesting to me. To my knowledge, he has never weighed in with his own theory or belief about why these disappearances happen. He does say that he doesn't think it's bigfoot ( a lot of the disappearances happen in national parks) or aliens.

He also gives a list of common characteristics of the victims. Usually in men their 20's, of above average intelligence, accomplished, and they don't fit the "normal" suicidal profile. Scary stuff but I have nothing to worry about seeing that I'm in my 30's, of average intelligence, unaccomplished, and suicidal. Just kidding about that last one.