A direct answer - because if you donate and work with people near you, you have to deal with the people. It doesn't sound like much, but it's the whole linchpin - you have to face the reality and often realize that what you want to do simply can't be done for any number of reasons, and then you have to back up and try a different tactic.

If you ship your money across the globe you can sit back and be content that it's working well based on the glossy reports you get; you don't have to actually deal with the people as people; just as statistics.