I don't think we as fans know everything that's going on behind the scenes. GSP may want the fight but he has a deal with under armor, while UFC makes their athletes wear Reebok. He might want higher pay that the UFC is not willing to fork over. There are so many factors here. I bet if the UFC could get a money fight out of Woodley, they would. But sometimes it's not feasible. So they go with the best they have.
Besides, Wonderboy is a treat to watch. Having him as champ is gonna be amazing. Machida 2.0. No can defend.