Why doesn't anybody know about the Law of One?

[caycegal]

For, the experience or sojourn in the earth is not by chance, but the natural spiritual and soul evolution of the entity; that it may be aware of its relationships to God--through its relationships to its fellow men; recognizing in each soul, as well as in self, those possibilities, those opportunities, those duties, those obligations that are a portion of each soul-entity's manifesting in a material plane.
Edgar Cayce Reading 2271-1

I think this Edgar Cayce quote shows a remarkable similarity to the Ra/Law-of-one Material. So the answer would be that a lot of people know about the material, just not always in the same specific format or coming from the same channel.