I think they're purposely stalling Rory from getting the title shot. Say they do Robbie vs Rory. Rory wins the title somehow in convincing fashion meaning no rematch. GSP then comes out of retirement. We already know they're not down to fight each other, but who is the biggest draw? GSP. Now say we get Lawler vs Hendricks 3. Hendricks wins, closing out the trilogy, and GSP then comes out of retirement to try and take the belt back. You couldn't script a better end of the year scenario for the UFC.
So basically, Rory's title shot hinges upon GSP's decision to come back or not come back...now that's power.