Insiders say that the locker room sentiment is that Punk decided to leave due to being unhappy with the way things are going, and a feeling of general burnout, rather than some sort of injury. Speculation is that it could also have something to do with stars who return as "part time" workers like Brock Lesnar and The Rock are getting pushed over guys who are full-timers with the company.
Punk did a recent interview with Ariel Helwani (MMA reporter) where he discussed the difficult schedule he's had for the past ten years working for WWE, with little to no time off.
It is noteworthy that Punk's contract is up this July.
Punk also sent out a cryptic tweet to his fans, "Thanks for all the support. Keep being you guys, it's pretty cool."