The issue is that people generally view their situation not by how much they have, but how much more they have than others. It's like a race to these people - who's winning isn't based on how close to the goal they are, it's based on how far ahead of the competitors they are. People who have everything they need often see others getting to that same point as competitors catching up, and, seeing that they are not advancing themselves, they feel that they need to prevent that in order to maintain their lead. It's meant to be everyone working together, but few see it that way, especially among the current "winners."