From what I see, that can be said for just about any demanding business. They eventually miss certain aspects about the job. The energy from the crowd, seeing new things, the fans, the money, etc. But it's hard to miss sleepless nights, appearance after appearance, getting banged up, the schedule, the traveling, politics like with any business, etc.
It's kind of a love hate relationship with demanding businesses. In order to achieve the kind of exposure, that rush and greatness they want, they have to go through the rigors of the business.
Guys like CM Punk worked hard and enjoyed the good parts. Worked hard to get to the top and be known. The opportunity came and he ran with it. But at some point, once you've reached a pinnacle, not everyone wants to be Hogan or Cena. Not everyone is treated equal. Triple H calls it taking your ball and going home when it gets tough, which may be true. But not every superstar is looking for the same thing.
I think it's more of a relief after the rigors. But I doubt that means they hated the business. But after receiving exposure, saving money and looking into other ventures, they realize there's more for them. Someone like John Morrison probably never wanted to be a Triple H and REALLY stay in the business. Heck even Shane didn't want to stay in the business as he had other interest to become his own man. Some superstars are meant to be Hogan, Cena, Taker, HBK, Triple H, etc. Some are meant to be there for a short period of time, fill the card, entertain the crowd, and move on.
I doubt CM Punk is COMPLETELY done, but my personal belief is that the rigors of the business and certain politics pushed him over an edge to walk out. I don't lose respect for him and don't see him as weak. Just another human being who simply needed a break. Stone Cold Steve Austin did it and related to it best…he said that for him and probably CM Punk, things just got hectic, he wasn't feeling the business and needed to just go away for a little bit.