Each day new steem is created at a rate that has to do with the current price and math I can't explain, but when the price is up the rewards pool slowly follows along the price trend, (Average of 30 days of price.) The new steem each day is distributed by voting shares. (That where the rewards come from)

After some amount of time, I really can't remember they will stop creating new steem. It is "down the road" though. (They used to say 3 years, but I don't know the current date)

In the meantime, other projects and opportunities may develop for future rewards, but it is speculation at this point.