If presented with a question, the lower courts must address it (even the Supreme Court must as well -- but they can simply, without additional comment, deny a cert petition so, in effect, they only have to address it in the most pedantic meaning of the word).
Sometimes addressing the question may consist of granting a summary judgement which precludes a trial, but the summary judgement includes a rational (sometimes little more than a rubber stamped copy of the movants' petition) for the decision and that decision will almost always involve interpreting the law (including case law). Obviously some of these interpretations are no-brainers (as in the example I gave), but they are interpretations nonetheless.
No (we hope) courts don't "arbitrarily" (re)interpret the law, but many cases do require subtle interpretations of the law and how it should apply even to facts that are not disputed by either party.