Ulterior motive
Readers and writers tend to fixate on novels' first lines, but last lines are just as important. More important, maybe, because they echo in the reader's mind for a time after the cover is closed. They are the author's last chance to drive home the moral, the truth, or the meaning behind the story. Where the first words pull you into the story, the final words get you to remember it and think about it.As such, they ought to be fertile ground for other writers who hope to write stories that have meaning.
Of not that, then they might just give you enough of a seed to grow a new story around.
I recommend Cormac McCarthy's The Road, Ray Bradbury's The Martian Chronicles, or F. Scott Fitzgerald's The Great Gatsby as great places to start from an ending.