Because Mercedes are awesome and Mansions are huge! I love having nice things and being a figure in the community! Why? I don't know. I work hard for my money and I do donate some of it but mostly for tax purposes. I am not Mercedes and mansion rich yet but I know I love stuff like that and I would be the same way.
It comes down to people being selfish. I am and it is not that I can't stop it. It's that I don't want to. How's that for humanity.