Poetry is one of the ancient arts, and it began, as did all the fine arts, within the original wilderness of the earth. Also, it began through the process of seeing, and feeling, and hearing, and smelling, and touching, and then remembering--I mean remembering in words--what these perceptual experiences were like, while trying to describe the endless invisible fears and desires of our inner lives.
The trouble with science fiction is that you can write about everything: time, space, all the future, all the past, all of the universe, any kind of creature imaginable. That's too big. It provides no focus for the artist. An artist needs, in order to function, some narrowing of focus. Usually, in the history of art, the narrower the focus in which the artist is forced to work, the greater the art.