Why does the US have laws that they don't enforce but they don't repeal?

Question

The State of Utah appealed the ruling to the U.S. Court of Appeals for the Tenth Circuit. Oral argument was held on January 21, 2016. The State of Utah was represented by Parker Douglas. The plaintiffs were represented by George Washington University Law School professor Jonathan Turley, acting pro bono.[23]

On April 11, 2016, a three-judge panel of the Tenth Circuit unanimously ordered the district court to dismiss the case on standing grounds.[24][25] Judge Scott Matheson Jr. wrote for the court, and was joined by Judge Bobby Ray Baldock and Judge Nancy Moritz.[25] The court relied upon the Utah County Attorney's Office policy limiting polygamy prosecutions to those involving alleged child bigamy, fraud, abuse or violence, concluding: "That policy eliminated any credible threat that the Browns will be prosecuted."[24][25]
Brown V. Buhman on Wikipedia

So basically there is a law against polygamous cohabitation. The law is unconstitutional.

Someone sued, and they succeeded. A judge declared the law unconstitutional.

However, even though the law is there, some other judges say that the person doesn't have any legal standing given that the prosecution doesn't prosecute those laws anyway.

I found this very bizarre.

Unenforced laws hurt the interests of the law abiding. It doesn't make sense.

Why have a law that punishes the law-abiding?

Answer 1

The concept of "standing" basically requires that you directly suffer some sort of harm from the act or law in contention; the exact details depend on jurisdiction (federal or particular state in the US). American courts generally do not hear cases in abstract, e.g. "I could be harmed by this in the future" or "I know a guy who was hurt by this" or "someone else could be harmed by it eventually". They require some level of concrete, discernible (and judiciable) harm that can be pointed to. As such, if a claim alleges harm from a law, then the fact that the law has not been, and will not be, used against them means there is in fact no harm for the court to consider.

That said, it is typically the case that the reasonable perception of a reasonable threat from an enforceable law is adequate to constitute standing. A lot of the legal challenges you hear about in the news right now frequently use this, as people challenge the Trump administration's actions on a variety of issues almost as soon as they are officially created. The distinction here is that there is no credible, current threat to these plaintiffs because the law is not being enforced in a way that could affect the plaintiffs. If the policy on how to enforce the law is changed, that situation may change and the plaintiffs (or a new one) may be able to make a new claim.

The ability for district attorneys and law enforcement in general to decide whether or not to enforce a law falls under the concept of prosecutorial discretion. Attorney generals have broad powers and responsibilities, and are expected to administer a just and effective application of their prosecution abilities. The US courts have routinely recognized an intrinsic authority for them to exercise discretion: they are not unilaterally and unequivocally bound to pursue all conceivable charges at all times.

On a practical level, there are issues of finite amounts of money and resources. The state and attorney general's office does not have the manpower and resources to pursue every conceivable case in every conceivable instance. It therefore must, of necessity, make judgement calls on which cases are worth pursuing and which are not.

Additionally, the mere action of pressing charges can have a substantial affect on the life of the defendant regardless of the ultimate outcome. As a (somewhat extreme) example, how many people do you think witnessed the acquittal of OJ Simpson and just decided that, yep, he's innocent, so time to treat him exactly the same as we did before this whole saga? A prosecutor has the discretion to not press charges for reasons including a low likelihood of conviction, and disproportionate impact on the accused.

And the judgment call on the likelihood of conviction will take into account the appeals process. So if the prosecutor suspects that a particular application of law, while permissible by the plain language of that law, would have a substantial chance of being overturned on appeal, such as due to constitutional issues, then they may also exercise their discretion to not proceed with charges. And this is what's going on here: prosecutorial discretion is being exercised to decide which cases of potential violations of the law might be worth pursuing and those which are not. Going by your wikipedia link, the financial limitations were a principle factor in this particular choice of prosecution policy. A reason doesn't necessarily have to be offered in general, as long as it doesn't run afoul of other rights (deciding not to prosecute any white people for a given crime would violate the 14th amendment, for example). In other situations an attorney general may conclude that a successful defense based on constitutional grounds is too likely in certain situations to justify an attempted prosecution.

Answer 2

There are a few reasons why unenforced, unconstitutional measures may stay on the books.

Politicians != Attorneys

The first, and most obvious answer, is that the attorneys defending a law aren't the same people responsible for removing a law from the books. Losing a court case doesn't automatically trigger legislative action. So once the court case is lost, we need to trigger some legislative action to remove it from the books.

Legislatures Are Largely Amateurs

The number of states with full-time, fully paid legislatures is smaller than you think. In most states, the amount of work they have to do is much higher than the time they have to do it in. In particular, you'll notice that a lot of those "funny laws" lists that makes the rounds tend to have a disproportionate number of funny laws from part-time legislature states. Why spend time and energy removing a law from the books that isn't enforced, anyway? And can you actually trust a part-time legislature to not do any unintentional damage to other state laws when they are just "cleaning" up the books for no real benefit?

Court Cases Aren't Ever (Truly) Final

There's a legal concept called stare decisis. We rely on it for the concept that, once a court case is decided, we can move forward, confident that we know the correct way to do things. That's practically the case, but it's not entirely true. Precedent, even long-standing precedent, is sometimes overturned. That law might be unconstitutional today, but it might not be in 10 years, 20 years, 30 years. At that point, that "unconstitutional" law that's been sitting on your books for a century can (possibly) be valid once again, and the legislature didn't even have to repass it.

Answer 3

Enforcing a law is a judicial process: That is, enforcing(or not enforcing) a law is up to the legal system. If a law is decided to be unconstitutional(a decision which, in the US, lies with the courts), then the courts can just decide to ignore it.

Repealing a law is a political process(and typically the same as passing a law): A legislative body has to come together, someone has to propose a vote, the vote has to be scheduled and so on. If there's no particular reason for any of the representatives to feel strongly(or at least, signal strong feelings) about the law, and especially if the courts have already decided that the law can not be enforced, then they won't put in the effort required to repeal it. After all, they(and their electors) no doubt have OTHER agendas they'd rather spend their time on. Since there's(arguably unfortunately), no particular obligation for the law makers to review, repeal or reaffirm existing laws, such laws can linger in the books indefinitely.