Because they cannot see the common humanity of those beyond their immidiate circles. We all live in concentric circles of relationships, and sometimes lose site of the fact that just because our lives are setup that way due to culture, society, social norms, religion etc, does not mean we shouldn’t question it, and try to be bigger then our collective constraints. As for the second part of your question, I believe we are only as wealthy as the poorest person on the planet, as satiated as the hungriest child going to bed on an empty stomach, as… You get the point. It’s because of I got mine you get yours mentality that we have the “have nots” strugling to get a piece from the “haves”. This the root cause of wars, terrorism, and I’d venture to say most conflicts in the world. So… we should all be proud to be what we really ARE: WORLD CITIZENS!