Perhaps a lot of Gate’s and Buffett’s increased generosity later in life is due to a natural inclination to be more reflective and giving as we age. Their consumption appetites are satisfied by a tiny fraction of their wealth, so they look around and discover how much good that wealth could be doing.
Come to think of it, the world might be worse off if they had decided at a younger age to discover philanthropy. All the money Gates and Buffett piled up in their 40’s and 50’s would not have materialized and be doing good things now.