You make it sound like he actually lost some money. It’s all just for show. It’s not like he wanted to buy something but decided to donate money instead. He can still afford absolutely everything he could even want. He’s not poorer in any meaningful way. The money his foundation has gives him power. Power to influence governments and policy (like he did with common core). His foundation has now more money than he donated so he has more power than before. It’s a PR stunt.