I don't have an answer, I've often wondered that as well.
What I always think about are FLDS polygamyst compounds where the girls are married very young to much older men with many wives. Whenever authorities intercede, the women don't WANT to leave.
But the fact is, they've been raised completely shut off from society. They are indoctrinated and brainwashed. They are not basing their decisions off of the real world, but off of a world of manipulation and abuse. And they'll raise their kids the same way and the cycle continues. Whereas if these cults were just forcibly broken up, sure it would be very difficult for the current generation who will see their families split up, but it would stop the cycle of abuse. It reminds me of when Jaycee Duggard was found. Her relatives made comments that her daughters by her rapist were angry that their father had been arrested and that their family split up. They had been born into that life, it's all they ever knew.
But of course, that is a dangerous approach to make such intervention legal. Because then it's a slippery slope of what behaviors are strange enough that the government can interfere "for your own good."
I feel this is a problem which just has no easy answer.
SC, I wouldn't chalk that up as just indoctrination. I'm sure some of those women would probably actually like to be somewhere else, but there are other consequences to consider.
Being killed by your own family because of not fitting some ancient custom is sadly a fact of life, and occasionally even happens in places like Turkey (see that girl buried alive recently) or occasionally even in the western world. There have been people who came all the way to the UK to murder their emigrant daughter for some unchastity suspicion. Because apparently a woman's having sex can be that unforgivable a stain upon the honour of the whole family. (And you have to remember that depending on which part of the world it is and how rural, even being an unmarried or divorced woman makes you a _probable_ whore.)
I'm sure that a lot of those women simply would rather stay with that old polygamist than wind up dead. Not a particularly illogical choice, nor one that requires brainwashing.
Then there is also the question of income. In a lot of the more patriarchal world, women are allowed very few jobs or even none at all. It's easy to say she should leave, but leaving to sleep under a bridge and beg isn't exactly the brightest prospect, all things being considered.
Also don't underestimate that "dishonour" part. A lot of those, if they leave an abusive relationship and decide to be the independent woman type, will be received with outright hostility everywhere they go. Even if they don't get killed, it can be a PITA to live in a community who thinks you're such an evil person that you'd even deserve death.
Worse yet, that dishonour literally extends to their family. The mother of a woman who decided to not live by the rules may herself be ostracized by everyone, for example. After all, she's the one who educated that "whore." (Which is another reason why they perpetuate the injustice.)
The presence of any children further complicates all those problems. From the economic aspect of raising them to the fact that they themselves will be tainted by that "dishonour" everywhere they go. You can get a woman to comply to a lot of nasty stuff if you essentially have her children as hostages, and in some of those cultures that's really what it is, by any other name.
Etc.
Basically don't underestimate the nastiness of some cultures, and how one can theoretically have all the choice in the world, yet really have no sane choice.
It's the reason why I find cultural relativism abhorent.