Like some have said; he's not spending his money right.
Being a billionaire doesn't just mean supercars, mega-yacht, jumbo jet and mansion; obviously with the wealth to buy all of that, you will just feel that ''you have done it all'', but not quite. Take a look at Bill Gates and Warren Buffett and their foundation; they're funding healthcare, education and nutrition programmes to help poor countries around the world, which keeps them busy and happy to help people; at least when they die, they have an honoured legacy. And they are the richest people on the planet, 20x times richer than that Minecraft developer.
And aside from donations, he can make political changes in the world with his wealth, in a good way obviously, which keeps him busy and makes him and people happy for his political changes.
Being a billionaire is everybody's dream, and no way anybody can be sad from having billions of money.