in general I find that "why did someone behave this way" is almost always answered by "behaving otherwise was too difficult and frightening for them at the time," and then you have to dig into why that is. people behave in ways that feel 1. easy for them (do not require much thought or effort) 2. accessible to them (patterns that have worked many times before) and 3. safe for them (apparently predictable outcome)
this is true even for behavior that is absolutely horrific and totally unacceptable. which can be a tough thing to accept, I think.
