Why is "Kubla Khan" called a fragment?

Coleridge's poem Kubla Khan is called a 'fragment' primarily bacause the poet himself chose to call it a fragment of a fuller composition in a state of dream, an account of which was supplied in a prefatory note to the piece on its publication in 1816, some nineteen years after its so-called mysterious genesis. The issue has been strongly debated ever since, and though the poem shows some elements of dream and a somewhat abrupt end, it is still simplistic to call it a fragment for it does not show any incoherence of construction or illogicality of thought. The centrality of the image of Kubla's 'pleasure-dome' through all the three stanzas of the poem holding the thought-process metaphorically together, Coleridge's natural-supernatural imagery, the thematic link between the two sections inspite of the geographical switch from Kubla's earthly paradise in section 1 to the song of the Abyssinian maid, & the poem culminating into a dicourse on the ontology of poetry rather suggest that by calling Kubla Khan a 'vision in a dream, a fragment', Coleridge palyed into the hands of critics.