At least then they would have to make an open argument for registration and by then all the 300 plus million guns in private hands would have no paper trail.
Registration is what they need to have confiscation - an anonymous background check gains them no ground and in fact would lose them ground as the paper trail from retail sales through FFL's would be voided in any real or legal sense as the gun could have been sold numerous times in paperless background checks that do not include information on the gun or guns that were transferred.
Right now they are pushing hard for registration under the guise of "universal background checks" - when we argue against that we are burdened to have to explain to most people that we are arguing principally against registration. That is fighting this current fight with one hand tied behind one's back. Our opposition gets to say, all we want is a simple background check and never has to defend registration. And it gives them an easier road politically to get registration than if they had to openly push for it.