comment: >
context: Why would they want to? That's like retiring from CEO and coming back as middle management. >
  
  I’ve actually known some senior level engineers that love nothing more than coming down to the lab and running through test cards with the technicians. When you’re at the top you lose a lot of the joy that comes from the basics. I’ll bet personal job satisfaction is much higher with small town mayors than with presidents. >
  
  For retired presidents they usually feel they can use their platform to focus on projects that are important to them, and only dip back into the world stage if they feel they can bring weight or influence to something. Carter and Clinton have both negotiated prisoner releases with North Korea, for example. Former presidents have also been influential in raising funds for humanitarian relief (Clinton and Bush Sr worked together after the tsunami in 2004). Also don’t forget that ex-presidents can make an absolute fortune for speaking engagements, and also on book deals. But really, for most people that serve as president, that was the culmination of a lifelong goal. They are ready to move on to something else. Eisenhower painted and golfed. Teddy Roosevelt hunted and wrote books. Jimmy Carter is a Sunday school teacher and builds houses.
  Other statesmen do occasionally get back into politics, and John Kerry is currently the special envoy on climate. After Mitt Romney lost his presidential election bid in 2012 he moved to Utah and was elected to the Senate and is still there. 
  There is precedence (though it was a long time ago) for former presidents to keep serving in other offices as you suggested. John Quincy Adams was elected to the House of Representatives after he left the presidency. William Howard Taft was appointed Chief Justice of the Supreme Court, and by most accounts he was much better suited to that role than the presidency. >
  
  Most people who become president do so late in late in life around mid 50s or later and after service are normally 60+ and economically independent >
  
  Because they all make way more for private speaking fees than they ever did in public service. >
  
  Former POTUS' bow out and leave things to the rest of us, seeing as it's no longer kosher for them to be wielding that highest power of the land, either vs. a sitting POTUS or over all the rest of us. Jimmy Carter's post Presidential service has been exemplary of a Man of Leadership since his leaving office. Mr. Obama and even more importantly, Mrs. Obama's service to the world has also been exemplary, with neither taking anything from successive Presidents yet not ceasing to provide leadership.