His reasons make sense and I think he realizes that at this point he's not going to be challenging for the title. Especially not anytime soon. He made dramatic leaps and bounds from his days on TUF but he's never going to crack into that top tier of fighters. His best was with Rampage & Franklin and he was outclassed in both. Losing to an up-and-comer had to be a breaking point.
He said he's been training hard for 28 years and his body is starting to tell him enough. It makes sense. Wrestlers go through some of the most grueling training sessions known to man and MMA is just as bad. I can only imagine what it would do to a man's body training that hard for that long. Might as well bow out now before there are problems later.
He'll always be apart of the record books. First disabled fighter in the sports biggest promotion and he didn't do half bad for himself either.