My considered opinion is that the main reason Bill Gates is spending so much money, is to improve the world just enough to generate more users of Windows, over

My considered opinion is that the main reason Bill Gates is spending so much money, is to improve the world just enough to generate more users of Windows, over decades, in developing countries, thereby adding to Microsoft's bottom line, in the very long term, and in doing so, making more money for himself. Think about it: You have to raise living standards for people in untapped markets before they can buy your product, a thing which they now effectively consider an unattainable luxury.