The reason is that there just isn't an ethical way to accrue a billion dollars. Stealing from workers labour is an inherent part of becoming a billionaire. Plus, usually some other exploitation too, like fucking others over with patents.

I would agree that there is no ethical way to become a billionaire, but I think that lacks context and scale.

Most billionaires make their fortunes from exploiting the labour and material wealth of the global south. Gates made his fortune by bullying the rest of silicon valley in the 90s, leading to the monopolistic tech market we know and hate today.

This is unethical in that scope, but when compared to global exploitation of other billionaires in the same tax bracket.... it's the best we could realistically hope for. Gates has essentially been unethical in the realm of wealthy 1rst world nations, all while directing a significant part of his wealth to improve material conditions in the places most billionaires extract wealth from.

Doing charity with a small fraction of your obscene wealth after this isn't any kind of moral absolution.

I mean 50 billion dollars is not just a small fraction of his wealth, and he's literally cured diseases that have killed millions of people over time.

Moral absolution isnt something that can be weighed and measured, it's subject to ethical belief systems that are not uniform across people or cultures.