According to the rumors, WWE wants Cena/Punk to happen because they don't want their WWE Champion (Punk) to be 3rd last on the card in what is supposed to be one of their biggest PPVs (since Cena will get the main event regardless of whether it's for a title, and you can't forget Triple H/Brock.) So, putting them together is a way of accomplishing that. It's a good idea, come to think of it. At least Punk will be getting the main event, unless they're overshadowed by Triple H/Brock.
It may also be a way to put the belt back on Cena and do so in a way that finally gives him his win over Punk. Disappointing that Punk's title reign ends to someone he's already beaten twice last year like Cena, but really, if Cena is gonna always be in the main event, then you may as well just put the belt on him because it does the titles no good to have them constantly being defended in the undercard.