Why do we tend to speak of Gertrude Stein as a poet? She was a poet, of course, but above all she was a fiction writer and an essayist.
The easy answer is that Stein was appropriated as an antecedent to the Language poets, a move that was instrumental in giving her the place in the canon that she has today.
But that kind of begs the question, because, after all, the Language poets themselves constantly pushed the boundaries between poetry and prose. My Life is often taught as an autobiography, for instance. And why not? It has sentences and chapters.
I'll be thinking further on this in the coming weeks. Ideas welcome.