SCOTUS can only act on it's own constitutional authority under Art III, S2, clause 1.
Therefore there needs to be an actual case or controversy before the court.
Under Bruen that controversy was the specific question:
Whether the Second Amendment allows the government to prohibit ordinary citizens from carrying handguns outside the home for self-defense.
So while it would be great to have tossed out the NFA and GCA, it simply wasn't before the court.
Art III, S2, clause 1 doesn't prevent them from tossing the other laws in Bruen. Their conclusion for historical requirements of preexisting laws de facto nullifies ALL laws not preexisting the signing of the constitution. It's a clear, logical extension
I argue they are in violation of the constitution and our rights for not striking down all laws that don't meet their new standard in the ruling.