Shouldn't they be having Cena feud with someone who would be next in line to challenge him for the Heavyweight belt?
Cena's also feuding with Booker and Show - that's the next PPV, and they're not going to bother to set up the next one till this one's over (or at least closer that way.)
If they extend the Champion of Champions idea through Survivor Series, they could avoid having a challenger for Cena up until the January RAW PPV with the Elimination Chamber. If things were to remain relatively static through then, you would have Cena, DX, Edge, Orton and Other comprising the 6 in the match for the title. Two from that match end up meeting a few weeks later at the Rumble, then you begin the Mania build-up. Barring injuries, they could actually have a thorough roadmap to Mania already in place on the RAW side.