I think that your understanding of what an image is might be a little limited. The poem might not exactly create a visual image of photographic precision, but do you really mean to suggest that it has no visual associations for you? I suppose that different people experience poetry differently, but personally, I found the work very evocative. The first line almost makes me think of an impressionist painting, with figures that don't have clearly defined features, but create the sense of a crowd of featureless people, with certain people growing clearer as the viewer's eye traverses the scene. And for me, the second line created the clear image of cherry blossom petals clinging to a branch after the rain. Perhaps you experienced the poem in a different way, but I feel that the imagery is definitely ingrained in the poem.