People love a "safe thrill". As part of the biological human need to survive, the psychology of acting out scenerios in which a "hero" (as stand-in for the average person) can resolve life-threatening issues is in the same manner children play house, play doctor, or play war to work out psychically -- in their limited experiences -- the anxieties of life as they mature. People are social animals.
Horror stories, with their various exaggerated monstrocities, would, therefore, be an acting out scenerio of the audiences' fear of "The Other", the threat of a stranger, or addressing a deeply-rooted fear of deformity (another kind of threat to survival -- a mutation which may harm the gene pool). "The Monster" is the repulsion within one's self, the opposite of attraction, and may be sexual in nature. If "Dracula" is about repressive Victorian seduction and "Frankenstien" is about Alpha male territory anxieties (including that of acting as God), why the "murder mystery"? What is entertaining about murder?
Perhaps the answer is in the development of the plots within the genre itself. Since one is satistically murdered by someone known (not a stranger), the fear of intimacy may be part of the audiences' emotional connection to the stories. Ultimately, in a "survival of the fittest" mode, who is to be trusted? To have the highest survival rate, one must remain an independant adaptable individual within a group where set rules of engagement are spelled out and expectations met. To kill someone is to love them, to care what they say, do and are, because ambivilance isn't a motivating force for anything.
Secondly, a parental figure -- a detective usually -- is involved in the resolution, someone who is smarter than the rest. This character's job is to reassure the audience of their trust in authority and assure the gene pool is safe. When children died of disease in the past, it left confusion to the surviving children and murder mysteries may be a way of making sense of the "randomness" of death.
Another aspect might well be that the "cupcake murder mysteries" genre is about a "mother" anxiety, using food as a symbolic gesture of reassurance, sensory recall (oral developmental stage), and reward. Is the culinary art murder mystery really about sibling rivalry, fighting over and murdering over food and needing "mommy" to rescue the situation?
As adults, the need to seek out these kind of mythic stories -- as pure fiction -- must have some underlying real-life reward or people simply wouldn't do it. From the primitive cavemen's fireside story-telling to the computerized Information Age inter-active games, the story hasn't changed all that much. The ultimate fear is of death, which, of course, is really about living. Dolce Vita di Libro has represented itself as not only a book club centering discussions on death, but in the promotion of living life to the fullest through lifestyle choices. The ironic juxtaposition of a "sweet life" in contrast to ugly murder and mayhem is the drama that Shakespear speaks of: all the world's a stage...After all, if you can't act out murder plots with friends, what's the point?