We have established the minimum requirement for OER of a permissive license. However, As soon as a work is created, it is protected by copyright.
As soon as a story is written, a painting made, a photograph taken, or a film shot, it is copyrighted. This means that the creator, or their employer, owns the intellectual property rights for the original work. Like other forms of property, the owner can sell those rights, trade them, or simply give them away.
This is why there are so many different open source licenses, and so many uses of the phrase open educational resources. The creator of the original intellectual property can follow almost any path they want to share, trade, or sell it.