I think it's because GSP cannot sell fights. He doesn't talk shit. He doesn't get mad. He doesn't do anything really to hype the fights. Kos is a loud mouth moron who will talk shit, make himself look stupid and get irritated because GSP won't play his mind games. GSP as champ brings far more money to the UFC than Kos ever will. This fight sold out in a 23,000 seat arena and is looking to have the highest gate revenue of any UFC event ever, all because it's in Canada. You know how they love GSP. He is a huge star up there.
I really think GSP will put on another clinic with Kos like he's done in his last 5 or 6 fights, but GSP can be rocked as evident from the Serra fight. Kos can hit hard and if he connects it could be all over. I look for this fight to be on the ground inside of two minutes with GSP on top doing his thing to avoid damage and still win rounds.