What does it matter how much he has left? There are somewhat diminishing returns spending money on philanthropic causes: if he were to spend 30 rather than 3 b

What does it matter how much he has left? There are somewhat diminishing returns spending money on philanthropic causes: if he were to spend 30 rather than 3 billion the result wouldn't be ten times better. I'm happy he's trying to make the world a better place while still keeping an eye on the money being used efficiently. Why does the 100k matter if the 3 billion don't?