The left uses the NRA as a talking point precisely because it is such a small minority of gunowners, and can be demonized as a small vocal minority of gun owners and citizens.
Alinsky's Rule 11: Pick the target, freeze it, personalize it, polarize it. Don’t try to attack abstract corporations or bureaucracies. Identify a responsible individual. Ignore attempts to shift or spread the blame.
The problem for the anti-gunners with Rule 11 is that their target actually is 150 million autonomous individuals, with no particular leader or representative that can be thusly targeted, frozen, personalized, polarized, and destroyed. We are the kind of diversity the left dreams of: men, women, children, and other creatures from every conceivable background, and not all belonging to any particular group that can be easily targeted and destroyed. We are that crazy, whacky super-majority of citizens and voters. No, that doesn't work so well as a talking point.
The "NRA" and its president can be individualized and attacked as such. That crazy, whacky organization of about three million people, led by this one crazy, whacky person. That works a little better for the leftist talking points, even though their whole side of the issue is a long string of losing arguments.
That is also why they have to attack "the gun", an inanimate object.
NRA currently claims a membership of 4.5 million. While magazine subscriptions suggest this number a tad inflated most agree on a number around four million and growing. Add to this number those thousands of nonmembers who generally agree and support the NRA agenda and you have a political force few politicians choose to ignore. If not for NRA supporters current laws regulating gun ownership would be much more restrictive.