Literature includes stories, poetry, and more. Literature is the writing of a time, a place, an era. Those ideas and assumptions which we breath in unnoticed are shown within the literature of our time, and the thoughts and ideas shown within literature help to shape the lens through which we view the world. Mythology is another aspect of literature, different from it, in my opinion, for several reasons.
Mythology tends to follow specific motifs, and also to have common characters within it.
Mythological stories tend to be written and rewritten by many different people in many different times.