6. Injury
John Cena certainly didn't look injured when tearing the house down with Seth Rollins at Madison Square Garden this past week. But pro wrestlers are the masters of covering things up, and there's speculation that maybe Cena's time off is due to a nagging injury. It could be a small surgery requirement, or just a chronic condition that needs resting up. Although logic says that WWE are going to be damaged by Cena's absence, it would make more sense to get such an injury sorted now before WrestleMania season comes around. So Cena working injured right now and taking time off to fix it is definitely a plausible theory.