Th's the hype that goes with it. Oscar's nice guy act and Floyd's badass act(both are fake,Floyd's actually not that bad a dude),the 24/7,the advertising everywhere,the media tours. Of course the average fan is going to buy it. They are also going to use these 2 angles:

Floyd Senior will be back to use the whole father v son angle and he trained Floyd and made him,he can break him.

And the fact that Oscar will have had a warm up fight then v Forbes,most likely.He will win and proclaim he is back to his best and the average fan will eat it up.

All these things will add together to make a fight which (unfortunately) will be as big as the first fight imo. Us hardcore fans who love boxing but are not here to be made fools out of/not rich don't account for a big % of the fans out there so unfortunately,this fight will still be a resounding success.