Replying. First of all I'm going to toss the idea of 'relative poverty' out there.
http://www.ask.com/question/what-is-the-meaning-of-relative-...
Second of all. If the people in Africa are so much poorer, it means that helping people in America is a much better investment because their opportunities to improve their lives and have a future (and help our economy) are so much better.
I seriously think at the end of the day it's a self centeredness that motivates people to go to other countries and help. They essentially want a cool story to tell their friends, not so much a genuine need to help others.
Or maybe you can't even blame the individual. Maybe in America we are so far from even knowing what a 'meaningful' life is, so we see people doing cool things on T.V. and say I'll buy that adventure and it will make my life meaningful.