Looking at how a law has been implemented in the past is a basic legal principle. The reason for it is to provide context as to the intent and proper way to interpret a law, in order to ensure continuity and consistency in it's application. The idea is that, all other factors being equal, continuity and consistency are desirable.

Though it is also a basic legal principal to determine if the circumstances that gave rise to a law are still in effect, and if not the law may be rendered moot. So much so that laws that haven't been enforced for an extended period of time can be challenged & overturned on exactly that basis if someone suddenly finds themselves on the wrong side of such a law. I'm just making that distinction though; In this particular case, there is still a continued interest in controlling what enters & leaves the country. The specific issue with this court case revolves around whether personal electronics are truly comparable to items that have traditionally been subject to searches. The court says no, they are not comparable, which seems to make sense: Such devices are less like cargo or luggage and more like personal papers, journal, etc.