It would have been 100% fully within his right to simply keep it all, or blow his fortune on snorting Fabergé eggs, or buying classic cars and crashing them.
Instead, he's giving almost all of it away. He's choosing to retain control over how it's given away? Well so what! It's still way better than keeping it all.
I am no fan of Facebook, but man, the amount of vitriol coming out about this move just astounds me. Giving away 99% of your wealth is apparently not commendable unless you do it just right. Meanwhile, how much are the commenters themselves giving away? Oh, somewhat less than 99%? Yeah.