Why do so many cultures have monsters that prey on families?

Question

While researching La Llorona and vampiresses, I noticed that lots of cultures have predominantly female monsters that use deception to prey on families. Lamia that prey on young men and children, deer women that seduce and kill young men, incubi that seduce and impregnate young women, aswang that prey on children and pregnant women, revenants of stillbirths and women who died in childbirth, mothers that seek vengeance for lost children or treasonous husbands, demonesses that cause miscarriage and stillbirth, ghouls or aswang that consume dead relatives, mysterious wives that turn out to be ghouls or aswang, mysterious husbands that turn out to be alligator men, mullo and strigoi that target former family, etc.

All of these monsters revolve around a common theme of losing family, particularly in ways that pervert the typical growth of family. Children die in the womb, at birth, or before adolescence. Spouses, adolescents and young adults are seduced away and either killed or defiled, even forced to bear demonic offspring. Mothers die in pregnancy or childbirth. The deceased are desecrated or return from the grave. Loved ones turn out to have been literal monsters the whole time.

Why is this such a common and enduring theme around the world? Why are the patterns so regular?

Answer 1

The family unit was like a religion to people in the olden days and the importance of family honour more keenly felt, even to the extent that anything (bad) that happened in the family might have to stay in the family for fear of causing a stink among friends' families and the wider society, which was, compared with now, a comparatively small community.

Any external thing that threatened the family would have terrified the average married man or woman as much as total social exclusion would have. Any unmarried person of a certain age might have once been seen as a danger to civilized society, because the human norm of marriage and kids was far stricter then than now, so, particularly for women, the unmarried life was considered suspect, and something to keep at arm's length. When a supernatural element is added it seems to become for them a potential nightmare.

Modern statistics show that a significant portion of crimes committed against members of a household are committed by family members or friends of the family, the like of which in the olden days would more likely have been covered up and never talked about.

Physical abuse, sexual violence, incest, abortion and inbreeding could be repackaged as supernatural horror. Honour killings were perhaps more common in those days, and wild tales too, so there could be an neat explanation for a death or miscarriage that implicated, say, some unattached woman who lived out of town and who was really a secret vampire, or perhaps an undead family member, or something.