The challenge with that is whether umpires will think that changing a call will make their fellow umpires look bad. Will they make the right call, or will they be more concerned about perception by their peers? All they're doing is watching the replay. We can all see the replays, MLB can see the replays and if the press box ump makes bad calls, he gets fired. If all you have to do is watch replays to determine whether the call was right and you don't do a good job, you don't keep your job.