I don't think it's religion that affected the whole event, it's his stance on gay people. As a fan of boxing and pacman, I've watched a lot of boxers from different religious background. Muslims, christians, buddhists, atheists, whatever else, their religion doesn't affect my decision whether to watch them or not. I watch boxing for the excitement of two guys trying to best each others skills and enduring pain and violence. Their personal life stories or beliefs only come as an extra to add drama to the battle.
I don't think Pacquiao "hates" gay people. He only believes they're going to hell or wherever. There's a big difference there, since hating someone doesn't really need a religion to back up your reasons, while simply believing someone's going to hell for their sexual orientation can still mean that the person actually cares for them and wants to "save" their souls.
Spirituality isn't really my thing, so to me, if there is heaven and hell or whatever, if you've been good in life and didn't hurt others with malicious intent, then you'd probably go to whatever is the better place after life if there is one
I really believe that it was just a mixture of Pacman's stance on gay people and Bradley's unpopular status previously which affected the sales. Don't forget that here in America, the economy isn't really that great and people would rather use $50 to buy one week's worth of groceries rather than watch two guys beating up each other. (I spend $10/week at Walmart to buy hotdogs)