Look, the 2A has a very weird history in the courts. There was no dispositive modern case on it at all. The 1920s Miller case was more procedural with a hint of decision, but had zero precedential value. Liberal and conservative law profs through the mid 1990s taught there was no precedential 2A SCOTUS case out there at all. Then in the late '90s, the liberals realized they could intentionally misread Miller to be some kind of "collective right" case (which it isn't; it's kind of based on the 2A being the opposite of all the liberals want the 2A to mean, and it's still not of precedential value).
For the 2A to get to the jurisprudence level of the 1A, say, it needed several things.
1) A federal case without state complications interpreting its meaning (Heller)
2) A 14th A incorporation or P-or-I case to establish the states are subject to the 2A (McDonald)
3) A case setting the level of scrutiny the 2A receives (strict, intermediate, or rational basis) <- WE ARE HERE
4) Cases applying the 2A with that level of scrutiny to various laws, arrests, actions, etc., dismantling or countermanding the violations thereof
The conservative justices are - as the court does in all such situations - handling cases where the lower courts flat out ignore Heller and McDonald where its worth smacking them down, while waiting for the circuit courts to weigh in on the scrutiny level in appeals from state and district court cases. They ideally get a split so they can chose among the cases, bring better than a barebones majority onto the decision, and unify on a rationale. Remember, Thomas "concurred" in McDonald because he did not like the whole incorporation approach and preferred the plain language Privileges or Immunities clause approach (which would have been a different approach than for basically any other enumerated right). Ideally they want to solidify a 6-3 decision, or at least have a rationalle-unified majority for the next step, which is KEY. I can't emphasize how important nailing down strict scrutiny for the 2A is. Anything lower than strict scrutiny on this enumerated right would not only twist a knife in the Second Amendment, but such a decision could put every other enumerated right into a "hey, let's see if the level of review really is stuck at 'strict' here" blender.
So they are waiting. We actually have a much better Court overall for originalism and plain language than the one that decided Heller, a case the NRA thought "we" would lose. Be patient. It took a good hundred years to go from "if you say bad things about the President during war, we can jail you" - and that was THE FOUNDERS - to the notion that the 1A actually might mean that's not cool.