From single-issue viewpoint, every case passed on relating to that single issue looks personal, venal, and crass. And are usually assigned vitriol appropriate to such notions.
However, the metrics are absolute. SCOTUS is presented anywhere from 3200-3500 case per year, and can only actually hear 700-800 cases at maximum. (For the 40 week SCOTUS 'year' that 20 cases per week--four per day.)
So, many "issues" do not get considered. Issues critical to those invested in them as single-issue controversies.
And, many minor cases get brought to SCOTUS, along with piles of pre-trial motions arguing procedure.
In this specific case, life-time bans on becoming a Prohibited Person is really an issue of the difference between USC and CFR and funding of agencies. To wit, a problem created y the Legislative and Executive ranches between themselves. 18 USC 922 was cooked up by Congress, and left to be administered by the Executive Branch (and by defunding portions of the law they themselves created). That's not really Constitutional--that's procedural.
Yes, there's an excellent argument regarding permanent disenfranchisement of free citizens being abhorrent to Liberty, but none of the cases brought that as an argument.
Just because a case is brought to SCOTUS does not mean it's properly framed as a constitutional issue--the NYC lawsuit being an excellent example.