In good mystery stories, the bad guys have a compelling reason for committing their crime. This reason is also called a?

Motive.

Explanation:

Mystery is a literary genre that is full of suspense. It contains a crime and the solution of it.

A good mystery writer always gives a motive to the criminal in his/her story. Motive is the compelling reason of criminals to commit a crime. In the mystery story, the investigator, the criminal, and all the other characters have motives. The motive of a criminal can be love, money, or revenge.

For example, in the short story "The Idol House of Astarte", the motive of crime committed by Dr. Pender was his love for Diana Ashley.

So, the correct answer is motive.