Hitting is really hard. If you feel up to it, and can find a public batting cage near you that has a fast pitch machine (usually maxes out 75-85mph which is 20+ mph less than your typical MLB fastball), give it a shot. When you hit the ball away from the sweet spot, especially on the parts closer to your hands, it really freaking hurts and throws off subsequent swings.
If the few players who are using this bat tend to hit that spot naturally, it makes a lot of sense to modify the bat to accommodate it, within the rules like they've done here. Hitting is super, super difficult especially today with how far we're pushing pitchers. Love seeing them try to innovate.
Plus, reminder, most of the team isn't using it. Judge clobbered the ball that day with his normal bat. Brewer's pitching is injured, and the starter that day was a Yankee last year and the team is intimately familiar with his game.