Shinsuke Nakamura is a unique talent, and the WWE is trying to treat him that way. A huge part of his character is that amazing entrance where he can show everybody what kind of a persona he has. His charisma is easily shown during those entrances. If you do them way too often, they will lose that special meaning that they have right now and that they had in NXT. They can’t afford to overexpose him.
Right now, this is in a great first feud for him as Dolph Ziggler is just a perfect opponent to begin with. He is one of the best in-ring talents that the company has on their roster. Ziggler will sell for Shinsuke Nakamura and will make him look like a million bucks in the process of putting him over while also giving the fans something to remember as far as how good the match between these two was.
Still, Nakamura needs that one huge win in order to really establish him as a star on the main roster. That victory that he needs to get is going to come from John Cena. Beating the main man in the company holds a lot of value. Cena is entering that part-time stage of his career, and it seems that he is willing to put over the new guys. He has done it with AJ Styles, and he is probably going to do it with Nakamura.
With his promos, Cena makes everything feel important, and every build up is great when he is involved. That is just what Nakamura needs right now, and WWE is not going to pass on the opportunity to put these two together and profit hugely with this move.