Honesty, Integrity and a sense of purpose that resonated with the greater public...among other things.
Well, All that is true. The REAL reason is he lived a good and fruitful life in this great nation that he could recall at will from his lifeguard days to Hollywood. He found love to be a tough measure and found his soul-mate. He found Horses to be very proud and happy beasts to help him relieve stress. He got to play roles in movies and sincerely get panned. He was a Great American.
I challenge you to find that in the field of candidates.