Because all the Amendments are subject to judicial interpretation.
The NRA has a particular view of the 2nd Amendment, that being that any law that would impede a law-abiding citizen from obtaining a firearm is an unjust restriction on a constitutional right. They want the ability to obtain that firearm to be reasonable (currently, it’s 72 hours subject to background check) and not six weeks with the right withheld if the person has, say, unpaid parking tickets.
Further, their view is that the right extends to all non-automatic firearms, and that restrictions on the type, or the ability to operate those firearms, also violates the constitutional principle. Restricting the right to, say, handguns, or anything that would throttle the supply of ammunition, is essentially unconstitutional.
And, they realize that on the other side, anti-firearm groups are working just as hard, and spending substantial sums of money, to increase those restrictions.
Bottom line: I am a 2nd Amendment person, all the way to the Glock 26 I carry in my handbag. THAT SAID, if ANYONE can figure out a law or a regulation that enables me, a law abiding citizen, to keep my Glock AND prevent these Orlando and Las Vegas types of abuses, I’m all for it.
But I don’t see how that’s possible.