I'm not debating whether the call on the field was correct, it looked clear cut. I'm debating the logic of the rule. Just bring the ball back to the spot where it's fumbled. Isn't that the rule other places on the field anyway? you can't fumble the ball forward and get yards to where it went out of bounds - otherwise people would just "fumble" the ball out of bounds every play to get an extra yard or two. It comes back to where you fumbled if it goes out of bounds.
As I understand it the logic goes like this. If the
offense fumbles the ball forward out of bounds it is brought back to keep them from using fumbling out of bounds as a strategy to gain yards. Should the
defense recover a fumble, it is placed where the recovery occurred (unless the defensive player was legally able to advance the ball). Therefore it is not the rule that you "
just bring the ball back to the spot where it is fumbled".
In this case, the ball was fumbled through the endzone which is a special case. If Pittsburg had fumbled out of bounds at the 1 yard line they would still maintain possession of the ball. The rule that the defense takes possession is to prevent the offense from purposefully fumbling forward into the endzone in hopes of making a touchdown. In the NFL this is associated with Dave Casper of the Oakland Raiders who apparently batted a fumble forward into the endzone and recovered it for a touchdown, winning the game. Since the offensive player's intention for the fumble, if there is one, cannot be determined by the refs, a rule was made to prevent it being used as a tactic. As to exactly why the 20 yard line is selected, my conjecture is that to place the ball at the point of fumble was thought to be less of a deterrent.