I sure it's been said, but some people are physically unable to leave. I remember Jesse Prince's testimonial where you shared that he had been tricked into joining the Sea Org and weeks after realizing it wasn't for him and demanding to leave, he was physically restrained, held captive, and required to do physical labor and attend classes until he was brainwashed into thinking he should stay.
I also remember reading years ago that one of the ways that circus elephants are trained is that they are tied with chains to tiny posts hammered into the ground. A baby elephant, no matter how hard it tries, cannot pull the post out. It grows up remember the frustration of pulling and how useless it was to resist. Eventually, when the elephant grown up, you can tie a multi-ton full grown adult to the same post. At this point, the animal could pull a thousand posts out of the ground if it wanted to, and could probably tear the place apart and escape, but it won't even try because of the conditioning.
I always think of that moment when Lisa McPherson was in the hospital after her public breakdown on the highway, when the doctors in the hospital wanted to help her, and even promised to protect her and keep her overnight, but she made the decision to go with her Scientologist "friends" who promised to take care of her - the exact people she was running from. And they took care of her, all right.
That makes me sad every time, whenever I hear her story, I want her to choose differently every time. Hubbard knew that if he got far enough into a man or woman's mind, Scientology would help them imprison themselves.