He and Mayweather don't get along, so there's no point in Pacquiao helping out the ratings for his arch nemesis.
After all, Pacquiao is quite the busy man, and something tells me he would probably have more fun signing karaoke at some random bar than watching Mayweather pummel Cotto.
It's no secret that boxing fans have long desired a match between Pac-Man and Pretty Boy Floyd; but the two parties have never been able to come to a full agreement, much to the fans' dismay.
Boxing needs these two fighters to face off against one another, but it remains a huge mystery as to whether or not it will ever happen.
Some might try to make the case that Pacquiao should watch the May-5th fight between Mayweather and Cotto for studying purposes, or in case "Money" loses.
If (and hopefully when) Pac-Man ever does get a shot at fighting Mayweather, he'll have plenty of time to study his opponent, so there's no need to watch this weekend.
What's more, the chance of Pretty Boy Floyd losing is pretty slim.
Yes, Pacquiao would be helping boxing by watching the fight, but he would also be supporting Mayweather, a boxer who has been so greedy about fighting against him.
Maybe one day boxing fans will get their wish. But for now, they have to settle for the two best boxers fighting against different people, which is why Pacquiao shouldn't show Mayweather the respect of watching him battle against a guy he's already beaten.