#1. Did not retire from WWE on his own terms: CM Punk

It's hard to believe that almost seven years have passed since CM Punk's WWE departure. His last appearance was at the Royal Rumble 2014, and a mix of factors, including burnout, dissatisfaction with his creative direction, and injuries, made him call it quits with WWE.
Had he not left, he was reportedly set to face Triple H at WrestleMania 30. But that never came to be. Years passed, and slowly, fans' hope for CM Punk's WWE return wore down.
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On multiple occasions, CM Punk stated that he had no desire to return to the ring, and the closest association he had with WWE was during his time as an analyst on WWE Backstage on FS1.
While CM Punk enjoyed the most memorable WWE Championship reign of the decade and had several accolades to his name, he considered it a personal failure to have never headlined WrestleMania. His legacy will be remembered fondly by WWE fans, but he's perhaps one of the biggest names who never got to retire on his own terms.