I came to think of a good analogy!

Steam is the guy that build up a stand on a farmers market and sells his goods and the goods from the people in his village that don't want to brother with the work to drive a hour to the city and set up a stand and stay there all ray long.

The steam guy does a service and keeps a agreed upon portion of the sales for his needs.

Its not rent, rent is what the steam guy has to pay as a stand fee.