People like Bill Gates aren't "random do-gooders".

Bill Gates was a software executive who got into malaria prevention and education reform and poverty reduction and God knows what else, not because of his deep knowledge and expertise in those subjects, but a generalised wish to become a philanthropist. He's the very archetype of a random do-gooder.

I'd not it find it strange that in the counterfactual that Bill Gates had the time to guard my own welfare (let alone some random African's), he might do a better job at it than I would myself.

But the whole point is that he doesn't have the time (or knowledge, or inclination, or incentives, or ...) to guard your welfare - or that of a "random African". Sure, if Bill Gates was my father he might be a better guardian of my welfare than I am. But he ain't.