Because that is what they love. Most of these people's wealth is a byproduct of their work. They were probably not working to get rich in the first place. They

Because that is what they love. Most of these people's wealth is a byproduct of their work. They were probably not working to get rich in the first place. They were doing it because that is what they knew best and were dedicated to it. It does not have much to do with money. Some poor artists work just as hard and that affects other people around them too. Hence the question should be "Why people (rich or broke) who found their passion can't stop working at it?"