I think another reason SCOTUS has not granted cert in earlier cases is because it wants input from the various circuit judges. Remember that, in many ways, this is "new" ground the Supreme Court would be plowing. The Supreme Court would undoubtedly like having the benefit of opinions from a variety of jurists before diving off the deep end.
Jim's Rules of Carry: 1. Any gun is better than no gun. 2. A gun that is reliable is better than a gun that is not. 3. A hole in the right place is better than a hole in the wrong place. 4. A bigger hole is a better hole.