The way it currently works in the polygamous cult world is that one wife (usually, but not always) is legally married to the husband. The rest of the “wives” are married in a religious ceremony but are single in the eyes of the law.
These days, most of the cults generally (there may be exceptions) wait until the woman is 18 before executing her religious marriage ceremony- it saves them a lot of legal trouble. The exception is the first, legal wife - who can be married at a younger age with parental permission, because she is actually getting legally married. This was the case with Elisa Wall, the victim in the case that put away Warren Jeffs.
There has always been a trickiness to prosecuting these plural marriages, because legally they are just extramarital affairs and prosecuting them just because the spouses participated in a legally meaningless religious ceremony smacks of religious discrimination - unless you start going after every couple that purports to be married when traveling together or checking into hotels.
I doubt that the leaders of the polygamy cults want legalized plural marriage, they like having it both ways. They get their multiple wives but they have no legal obligation to support them or their children - the cults usually expect the wives to go on public assistance as single mothers.
I’m not sure that fully legalizing polygamy is a good move, but I think some form of decriminalization would be a net positive to the women in these cults.
The stigma and legal gray areas surrounding polygamy serve to further isolate the cult members from society at large. Some cults, like the FLDS, physically isolate their members in communities controlled by the cult. But the FLDS isn’t the only cult out there and it’s not even the worst. There are other large cults whose members where modern clothing and live the cult life inside the larger secular community. They may only shop at cult owned businesses and live in cult-owned apartments , but those businesses and apartments are indistinguishable to an outsider from non-cult businesses.
These cults (I’m thinking of one called the Kingston Group as I write this, but there are others that are just as bad) hold their members in economic slavery. They work for cult-owned businesses, their paychecks are deposited in cult owned banks, their pay is converted to credits that can be used only at other cult businesses and they are not allowed to freely access the real money that is in their bank accounts - they need to convince the banker that they really need it, then the banker may or may not decide to give it to them. Even if a woman’s husband sets her up in an apartment, the cost of that apartment is deducted from her account. Children are expected to work and charges for their room and board are deducted from their pay. Good behavior is rewarded by good jobs and extra access to money, disobedient members are often sent to work on the cult ranch or in the cult’s silver mine.
The cults also engage in payroll, tax and welfare fraud on a massive scale, and because the groups are so insular, they frequently get away with it.
One thing that helps them get away with it is fear. They instill fear in their members, fear of government and fear of prosecution and persecution. And this fear of persecution and stigmatization keeps cult members from reporting crimes and seeking help from legal authorities. High profile polygamy prosecutions were used to whip up fear and increase isolation. I think if you remove those stigmas it’s the first step towards opening these closed communities and curbing other abuses. It may not help much, but it’s a start,
The sexual abuses that take place inside cults are not the only abuses and IMHO, the financial abuses are far worse. But they lack the lasciviousness that make them newsworthy. “Cult leader arrested for facilitating sex with underaged girls” sells, “Cult leader arrested for fraudulently obtaining millions in federal funds for non-existent businesses” puts people to sleep.
FYI, there are plenty of other noxious cults that arrange marriages and exert total economic control over their members but don’t practice polygamy or kinky sex practices… And they never get any press, because if there’s not a sex angle, it’s boring.