Simply by having a billion dollars means they have decided to hoard that wealth. They could give away 90% of it, leaving them with $100 million, it wouldn’t impact their quality of life in any way, and still leave them with more wealth than 99.9% of the planet. Imagine the good that $900 million could do if it was put to good use rather than sitting in a bank account as a status symbol - having the capability to do that good with no impact on yourself or your family and choosing not to makes you an immoral person.