Eh? Even if he paid a 50% tax rate throughout his life, he’d still be a multi billionaire.
And taxes in the US don’t typically end up in the developing world.
“In fiscal year 2020 (October 1, 2019 - September 30, 2020), the US government allocated $51.05 billion US dollars in economic and military assistance to foreign countries. Of this total, $39.41 billion dollars was spent on economic assistance, $25.64 billion of which was dispersed by USAID.”
https://en.m.wikipedia.org/wiki/United_States_foreign_aid
To say that the US doesn’t do foreign aid is just disingenuous. Also to assume that Gates only pays taxes in the US is also disingenuous.