[theknarf]

There's a limited number of resources on the earth. There's limited farmland, limited land for property, commercial properties, etc. Then there is limited amount of water, precious minerals in the ground, oil, etc.

If one group of peoples wealth increases a lot faster than everyone else then that means that over time they end up owning a bigger piece of our limited resources. The natural outcome of this is the same thing that happens in every game of monopoly, some people end up owning everything, while other people have to rent everything and have nothing to own of their own.

Imagine being born into a world very everything (land and other resources) are owned by a small group of people and you have no outcome in life where you could ever own anything? Never buy your own house, never start and own your own company. A world where everything is divided at birth between the people that own this world and the people that don't.