John Cena's brutal storyline murders go hand in hand with the last slide. Cena is the king of destroying not only young, promising Superstars, but also interesting storylines.
The Nexus took the WWE by storm a few years ago, demolishing Superstars and even the ring. Nexus was one of the most interesting things going on in the WWE; a number of exciting youngsters looked ready to make a huge impact on the world of pro wrestling. Until Cena got involved. He outlasted them in a 6-on-1 Handicap match and eventually played a huge part in their demise, killing the entire storyline.
Now, The Shield is tearing up some of the biggest names on the WWE roster, planning sneak attacks on Ryback, Sheamus, Randy Orton and John Cena. Just as the Shield is starting to heat up, Cena is put in a match against them at Elimination Chamber, which he'll most likely win because he's on a team with Ryback and Sheamus, two of Vince's biggest babyfaces.
Because John Cena almost always has to win, especially in big matches to look like a super hero, the rest of the WWE are suffering. Every time they find an interesting angle that the fans love, they involve Cena, who can't get beat by, in The Shield's case, three young kids, and the storyline dies.