Mechanisms -- good point. I have another way of putting it.

In TV police shows, detectives try to establish a suspect's means, motive, and opportunity for committing a crime.Sloppy detectives (and jurors!) tend to focus just on motive and its lurid details. In evolutionary bio/psych, we try to establish genetic variation, selective advantage, and heritability. Sloppy evolutionary hypotheses tend to focus just on the selective advantage and ignore the other two.

People are drawn to stories. We give evidence extra weight if it comes in the form of a good narrative. (Is there a name for that bias?)