Well that is a very complicated question. I would honestly say that it is because some people in this world are very greedy. Take the queen of England for example. If she was not greedy why would she live so lavishly while she well knows millions of children starve to death and live in poverty every year because of the life style that "capitalism" has created. While she could sell the carpet she walks on and feed many young children. It is because the rich think they are "superior" to the poor and rule down upon them with military force.
It is that same question that started world war two for all the wrong reasons against the wrong people.