But if he throws it and it had been complete, maybe he wouldn't have been forced into a Hail Mary at all and had a shot to get into FG range. If he had just thrown it away in fact, he might have had a Hail Mary that wasn't from so far away that he couldn't even reach the end zone. Even if the ball is caught on that last play, they don't score.
There is a time and place for everything. 51 seconds to go with the clock running is NOT the time to take a sack, damn the torpedos.