What is the most likely reason why the author does not include a resolution?

It's leaving the ending up to the reader.

Explanation:

When an author doesn't resolve a story they want you to think deeper about what might have happned, they want you to come up with your ending for the character/s, they want to see if you were paying attention to the story and find out what might or might not have happned. Hope that makes sence! Also sorry about the typos I can't spell well.