“Guilt or shame about previous silence. Oddly, guilt or shame about not speaking up sooner can be another powerful factor that keeps people from acting, even once they let themselves recognize that something is not right.

Imagine you get a new job and in the first week you ask your boss about a minor but questionable expense on his expense account. He tells you to ignore it, that it’s OK, and you go on to let similar questionable expenses pass by each week. A year later, when a company audit raises the same questions, you find yourself trying to defend your boss’s actions to keep yourself from looking bad.

Realizing that you’ve tolerated inappropriate or harmful behavior over and over tends to make it much harder to confront the behavior in the present. People tend to feel like they’re partly responsible, and come to have a stake in pretending or even believing that the behavior must have been OK.”

https://1in6.org/common-questions/why-do-adults-fail-to-protect-children-from-sexual-abuse/

This article while not using the world cult does explain some dynamics at work in cults that fail to protect children.