Because it wasn't before them. Heller involved Federal law. The Constitution gives the Congress exclusive legislative authority in The District of Columbia. Hence the question in Heller was "may the Federal government ..."
Courts decide the case before them. In Heller there was no question of state regulation of firearms. That situation is reserved for such a case. Judges don't decide issues not before the court.
Jack
If that is true, why does their decision which is always limited to the case before them, always wind up being the law of the land. Well at least those decisions that promote perversion.