And I suppose you belong to the superior race-*ahem* culture that is capable of innovating, and you can't understand why anyone would waste their time with poor Africans who won't ever amount to anything. That's what you believe, isn't it? See, if you really thought it was about culture, it would make sense to provide education where it was needed most, since education is perhaps the best way to overcome deficiencies in the culture.
Zuckerberg and Gates could invest more in America, but they don't owe it to Americans simply because they made more money off of Americans. (Or if they do, you should be arguing for higher taxation, not complaining about where they focus their personal cash.) As far as efficiency of altruistic efforts, it's pretty clear that a dollar will go a lot father in impoverished countries than USA, even when accounting for corruption.