Do you think anyone would be happy living in a world where a few have access to all the world's resources and others have essentially no access? Wealth is a essentially a claim on a share of the world's resources. They are limited.

Edit: To put it another way, imagine growing up with siblings that had the full run of the house, three square meals a day, free use of all the toys in the house, and control of what you saw on any given screen and the music you heard, while you had a single toy, a single meal each day, and were confined to a room that you had to share.