Explanation:
In the common law, when a case is decided, it does not only provide guidance on what the law was, it establishes going forward what the law will be. Meaning, it has a force of its own.
So that, when a state court decides what rights a lessee has, that becomes the law. Other courts will not use it as only one indicator of what the law is, but will follow the previous case- because it was already decided, and has a force of law. (This is all post-Erie, for those of you who care. Pre-Erie we may have to say a different pshat.)
For example, if Justice Marshall had written a constitutional treatise, and had claimed that the Supreme Court had the right of Judicial Review, but Marbury v. Madison had never happened, nobody would have listened to him. A later court deciding on the issue for the first time would go whichever way it wanted. But since it was a court case, it became the law.
There is absolutely no comparable notion in halacha, and that is the integral difference between how we learn halacha, and how those backwards people study law. There is no greater weight to a teshuvas haRashba, than the chidushei haRashba.
That is why we mainly study treatises, and don’t have huge compilations of ?”?? from every din torah ever decided, and every shailah ever asked. Treatises are much easier to read from. The shulchan aruch is not a restatement of prior shailos and dinei torah, it is a restatement of prior treatises. Specifically, a restatement based heavily on the tur, which is based heavily on the rosh, etc.