To be fair, we didn't become conscious of uiquity of fucking children (and that it might be causing irreparable harm) until the late 20th century. Before the 1990s in the US, it was a social convention to let each household raise kids without checks, so if you hear violence from your next-door neighbor's house, you leave it be.

The term incest technically covered any familial sex, but in the 1970s when discussed was about daddy (oft inebriated) having his way with his daughters. It was assumed child sexual assault typically was of this kind (and everyone's doing that) so it was disregarded. (other pairings were going on, but we made Alabama jokes about it. Or Mississippi jokes.)

Then it came up in some public cases that not dads and not dangerous strangers, but other familiar adults (teachers, caretakers, ministers, etc.) were getting handsy with the kids. When it was investigated it was found to be so ubiquitous that there were concerns full prosecution of all the child molesters would drastically reduce the workforce, and cause an economic crash.

This was the backdrop for the 1970s-1980s Satanic Panic, because we just couldn't process that everyone was diddling kids (1in 3 women and 1 in 5-9 of men in my generation were sexually assaulted as kids, and it's intergenerational ) so the whole story that satanists were ritualy sex-abusing kids became popular, inspired by The Exorcist and the Hollywood Satan-movie knock-off craze.

For more fun and existential horror, check out the Behind The Bastards pod two-parter on The Satanic Panic.