A bit young for it but he probably got assurances about a post fighting career with the ufc. Did he say why he was retiring?
Well if i was to guess I'd say...
He probably makes as much commentating as he does fighting. He probably thinks he's gone as far as he can go in MMA. The UFC probably have other things lined up for up such as ambassador type roles.
He's one of the most likeable and respected guys in the sport. I think he's made a good call and I wish him all the best!