This is an omission but not a fault in the book. He does not say whether art is rare or common in the speakings or writings of people. Later I will try to clarify this, via a concept of literature, specifically oral literature, which includes exactly what Zolbrod means by poetry. His book is not a sample of works from the whole continent. Actually, anthologies need a book such as Zolbrod's for perspective.
Anthologies are too much like contests.
To be included in one is to win a prize. But from Zolbrod we learn that thousands and millions of works, never written down, were someone's good art. The anthology winners are only the ones that went to town, so to speak. More on that later. His most prominent point relative to anthologizing, which will get us where I want to go, is that great care must be taken on the matter of orality, that is, on how to write spokenness onto a page.