Earlier quoted context omitted.
A CNC is something that is pitifully easy for a regulatory agency to track, as far as large numbers of purchases go. See: that fellow who was milling AR-15 lowers and just got busted. We're talking about the difference between machining metal, and downloading and printing a schematic. I hope that you do see the difference.
It is easier to track distributing a sold product. It is very difficult to track what a person makes in the comfort of their home. I dont think the federal government keeps a registry for the purchase of milling machines.
3D printing is presumably going to become ubiquitous, and require no skill or experience to operate and maintain.