The reality is that this crime does occur in the USA Canada and elsewhere. This practice is confined to small communities and government will not go near it for obvious reasons.
The Bolsheviks in the MSM will present this as a Mormon problem. Mormons are White Christian
conservatives and their women are photogenic.
The media can find stories of Muslim polygamy in the USA with ease. The problem is they do not want to and it is easier for the government to ignore the law. On a practical level this would be breaking up homes and relationships. This is not what any government agent wishes to do.
On a practical level even the most personable officer will go after people with fake divorce certificates. The entire second relationship is predicated on fraud, so even if there are children in the second relationship the marriage is fraudulent.
Part of the problem in Canada or New York is a social workers paralysis. We want people in need of medical care to get it. We want children to go to school. We want crime victims to report the crimes. All of the above will see and ignore polygamy in view of the larger goals.
The question is what would you do if you find it. Is breaking up families really optimal? Are we prepared to pay additional welfare costs? Are we prepared for the costs of denaturalization and deportation? Most of these cases involve a man creating a lie that causes adverse impact on the wives and children left behind. We are often penalizing wives and children for behaviors they may not be willing participants in.
Many questions have easy answers but this is not one of them.
What does one do if anything to the participants in a polygamous union? Whose interests are we
serving societies, the child's or someone else's? It is one thing to talk about theory but the real world is more complex.