I think they named it that because they couldn't figure out how to make the movie end. My theory is the writer made a note of "how it ends" on a draft of the script because they still had to come up with an ending, but the producers and director confused it for the final draft and ran with it.

It doesn't really work when you make a disaster movie without ever explaining what the disaster is. When it makes you laugh when the credits start to roll, you know your post-apocalyptic thriller has fallen flat.