Because at some point, everyone wants to retire and scale back the stress and obligations. Travel, enjoy his grandkids, yell at other peoples' grandkids that are on his lawn, tell people to stay off his "propity", eat icecream and red wine for dinner, not get yelled at by fans, not have to read stuff from fans about how worthless he is, etc.
Many are already retired by his age and certainly by 71 or 72. And those that aren't retired usually have really scaled back on their job duties and don't work full time.
Maybe Loomis is the exception, but I doubt it. I've know many old men that had carte blanche in their business and still retired. At some point everyone gets too tired of dealing with other people's crap.