Notice that none of the young women in the Cleveland house of horrors seemed to suffer from Stockholm Syndrome, although, apparently Patty Hearst did. (She was repeatedly raped, but it took weeks or months.)
My thinking is that in the ten years they were there surely they could have found a way out. He wasn’t there 24/7 - but then maybe they were so toughly cowed or something.
PS - I read about Patty Hearst and some things didn’t ring true. The pictures of her at the bank suggested to me that she was part of it. Her stance for one thing. I feel that she wanted to be part of that group.