Being 25 years old and a net worth of 100 million, he just may not have that motivation to excel at that elite level anymore. You gotta love the grind and the pain to reach the pinnacle of that mountain.
Golf at its heart is a game for masochists and control freaks, especially at the highest level. Because golf is a solo game, with no defender to stop you, no opponent across the net, no coaches scheming against you, the ONLY measuring stick is how you feel your game is progressing. "Winning" matters but its just superficial, since that is just a comparison to others that you really have no ability to control.
Tiger could've easily smashed all the records, but he decided he needed to change, for whatever reason that, as onlookers, may look crazy to us. Same with Spieth. It's a lifelong pursuit for perfection that, as Tin Cup aptly said, is never attainable. But that doesn't stop the effort.
My g/f who is from Osaka finds it quite cute that I have a play on Low Asian with Matsuyama as she thinks it is because I am doing it for her by supporting a fellow Japanese, so who am I to ruin it by telling her it is all about the $$$ LOL