The reasons for this are not hard to find. Indeed, you hit the nail on the head in the next paragraph by pointing out the role of governments.
> I'm not sure what can be done on that or what that means, just a bit breathtaking how governments can help people or really screw things up on a scale nothing else even comes close to.
A case study of this in Ethiopia serves as a point in William Easterly's critique of "technocratic aid" in general and Gates's approach specifically: http://www.seattletimes.com/opinion/guest-the-flaw-in-bill-g... He elaborates upon this at length in his book "The Tyranny of Experts: Economists, Dictators, and the Forgotten Rights of the Poor".
The way I like to think of it is that money, especially in large sums like the $50 billion in the foundation, is a potent tactical weapon. However, wars are not won on tactics/technology alone, but also on strategy. Here that amounts to solid leadership/deployment of the capital. I think this letter shows that they have done a pretty good job with it. Nevertheless, it is easy to fall into complacency and arrogance here. I only hope that they continue to listen, observe, and learn.