Because there are more lives to save and suffering to reduce in that far off land than in your own country, perhaps?

Are you, say, a man? Then why would you give anything to a charity that helps women? (Or vice versa.) Or are you perhaps white? Then why would you give anything to a charity that helps people of colour? (Or vice versa.) Etc, etc... Get the point yet? If not, I'll spell it out for you: "Charity" that only benefits copies of yourself isn't really charity.