Because its not about just having someone that you think will stay undefeated. Though that is a safe pick to chose it isnt always the smartest. If you pick a lesser known guy who you have a feeling will be fighting bums then that is a much better pick. Especially if you expect him to be super active.
Also remember that he is about to clean out the division. There is a good chance 2011 will not be a active year for GSP.
Title fights > Bum fights.