Firstly, because literature is a “work of words” (Dylan Thomas) and the words on the page of any given version of the work – a manuscript draft or different print editions – will exist in the several different places where those versions are located at once. They are not one artefact.
Secondly, even if we grant that the literary work is not identical with the historical artefacts in which it is dispersed, it is still not clear in which way the work itself is one, and not a multitude of variant versions confusingly labelled with one title. Strictly speaking, a literary work is not one work.
Thirdly, the “work” in the phrase “literary work” is best understood not as a noun but a verb. And since literature is always at work, it is not an artefact completed in the past and hauled into our present, but the continual reshaping of the past into a present. It is not historical but history itself, in a nutshell.
Thoughts fallen by the wayside 