I was talking to a friend of mine who follows racing. He's just as baffled as everyone else. He said none of the theories -- disruption in training (my favorite), missing the Winstrol dose, missing whatever other meds New York might not allow that other states do, the track surface, nothing -- can explain why a horse that could win the first two legs of the Triple Crown without seemingly breathing hard would be finished after galloping the slow opening mile of the Belmont. Unless he stood in his stall the whole three weeks eating the horse equivalent of Cheetos, he just wouldn't lose that much conditioning.
So, unless an explanation like Spectacular Bid's safety pin turns up, we'll probably never know why Big Brown just didn't run.