A common misconception is that if somebody openly licenses their work, that they are giving away all of their hard work for free. While it is true that they are waiving some of the "protections" of a traditional all rights reserved copyright license, they still retain the ownership and moral rights to their work (something that is taken away if writing a textbook for a publisher). OER authors often enjoy more freedom to use, share and adapt their own works than they would under a restrictive license with a publisher. In addition, all Creative Commons licenses require users to attribute, or give credit to, the original creator unless the creator instructs otherwise.
In most cases, OER authors are paid for their creation through grants, stipends, non-profit organization support, or release time. Creators do not get royalties like they would by going through a textbook publisher, but they are usually not creating OER free of charge.