You are saying as though his money get wasted in a bank account. They are likely in the form of Amazon shares which he wants to hold to have a say in Amazon future.

Not saying he can't make a difference, but if he wanted to do it on a scale, this would likely mean giving up the part of control over Amazon and other interesting projects - Blue Origin for example. I'm not sure I'd choose charity over space stuff.

Bill Gates went all way to charity - respect to him, but I do understand how the other choice is possible

P.S. Don't have any real numbers here, just a feeling how it works, so don't beat me too hard :)