Just like I said, Judah at his beat aint no slouch, but Mayweather proved to be the better suited fighter. Judah did have Mayweather's number in the early rounds (And actually should have scored a knock down on Mayweather), but this is the difference. Judah relies on his athleticism way too much because he's not that good defensively so he wastes more energy, and Mayweather is a fighter with a better defense and knows how to adjust as the fight goes on and is the better counter puncher prepared to fight 12 rounds strong if has to.
Early on when they both were fresh, they were evenly matched to everybody's surprise, but Judah had the slight upper hand because everytime Mayweather threw the right he had to reach, which put him in position to be countered which is what happened early in the fight. Mayweather also got hit with punches he didn't even see coming which is gonna happen fighting a speedy south paw. What turned the tide is when Mayweather took advice from his corner which was two things, 1. Walk Judah down and throw punches because it would cancel Judah's speed and he can't fight going backwards, and 2. Go to the body which by the mid rounds slowed him to a crawl and left him vulnerable to Mayweather's onslaught. The low blow was definitely done on purpose. That stopped Mayweather's momentum because he was on the verge of hurting Judah badly and Judah was trying to bail him self out which is exactly what he did. He'll take a 12 round defeat over a TKO anyday of the week.
The rematch will definitely end quicker because Judah's defense has too many holes and I believe Mayweather would be more agressive leading to a knock out midway.