They have tons of room to grow. They just choose not to.
Turn him heel & create another star, CM Punk rivaled his merch sales when he got that little midcard title push back in 11'. If he was given a super Cena push imagine how much he could sell.
Plus thats probably revenue not profit.
Ratings have declined immensely since 06 (when Cena really took over, and with Cena shoved down our throats endlessly in 11 & 12, look how low they are. And this year its probably going to be just under 3. It hasn't been this bad since RAW started. Since the in your house era.
His character is making money sure, but look how much money they are losing by having him on top, look how many people have turned away cause of Cena & years of stale product. Plus you don't have any other stars who can draw really other than Cena, Punk & maybe, when around say 06 there were lots of top stars.
http://forum.bodybuilding.com/attachment.php?attachmentid=5233723&d=1357051019