I think you missed my point. They can control ordinary firearms to some degree, though not perfectly. And nowhere near as effectively as printed firearms.
There is limited control because there is a benefit to some people to allow limited control. If they were not legal, they would all just move like drugs or alcohol during prohibition. It is an illusion of control that only exists because it makes life easier for a lot of people than going the underground route.
I suppose it all boils down to whether you think expedient manufacture and distribution is of any importance whatsoever.
For some reason you believe it is harder to move a normal weapon than to move 3D printers and printed weapons. There is no reason for that to be true.
Even if they were, they wouldn't be able to produce more en masse.
Why not? There have been a variety of stamped metal designs in the past. They are quite simple and quick to create.