2. They Need To Look Powerful, Not Invincible
The Shield has been named by JBL as possibly the greatest three-man tag team in WWE history because of their ability to work brilliantly as a team. Their victories so far have allowed them to be seen as resourceful, strong and talented. Their ambushes on superstars during promos and after matches show that they are prepared to bulldoze anyone on their way to the top. Put any more wrestlers in the Shield therefore seems a bit superfluous at the moment- they are currently an unbeaten tag team ( if one doesn't count the Cena DQ on the last Raw) that has taken on and beaten some of the biggest names in the industry. To add another name would actually be worse than do nothing- it would actually make the Shield seem too powerful- thus making much of their matches boring. One could see this problem with the nWo in WCW as they began recruiting more and more guys to the fold and thus stagnating much of the angles because the nWo seemed to be too big to fail. Furthermore, when a heel stable does become too big to fail, it often does no favours to the babyfaces who contribute to its downfall. Take the Nexus for instance, whose reign of terror managed to brutalise many of the top superstars in the business but in turn was halted by ( mostly alone ) John Cena. The fact that Cena succeeded where so many superstars had failed in breaking up the Nexus did nothing for his credibility simply because many fans believed it was just another example of Cena winning whatever the odds. And speaking of the nWo, that leads me to my next point.