Well in hindsight, I think even Arum knows that Pac is going to lose that match due to the judges. You can see his reaction when Pac lost to Bradley in their first fight which was also controversial. Arum raised hell during that time. However, when Pac lost against Horn, he did not even blink. He is just milking Pac until Pac hits retirement.
Bob Arum is trying to milk Pacquiao to the last drop. How we wished that rematch with Horn would have happened sooner than later because as Pacquiao is getting older, Horn is getting more matured and gaining more experience. But whatever happens, win or lose, Pacquiao would still have his fair share of the earnings, so would Uncle Bob. It's all business for these guys nowadays, because both Pacman and Bob Arum are in the twilights of their career and life, respectively.