Keep in mind there are THOUSANDS of cases per year that want to be heard by the Supreme Court. And they can only do a couple dozen at best. It's a simple matter of odds. Gun rights aren't the only important issue in this country that requires the SC's attention.
They're not our personal arbiters of gun rights. They still have to maintain an image of impartiality and legitimacy. If all they hear are carry cases brought before them by pro-gun groups. Then suddenly they look like some one-issue activist court. They try very hard to avoid that since it seems the Supreme Court is really the only branch of our government that still has any shred of respect and dignity left in the eyes of the people.