Sure, but legal processes aren't quick. I would assume they're trying to be thorough in the process. Probably not a great sign they letting the rule stay but in theory it doesn't actually do much. 80% manufacturers can still sell products. I can still buy an 80% or a 3d printer.
The real thing would be to just get a ruling to limit how they can change law through changing definitions. Same reason slapping down the bump stock was needed.
Also the issue there ruling on probably won't actually be a 2a thing but about the rule making effectively side stepping the legislative proceess.