Many of these are legal, you just have to declare them as such. For example, you can not saw of a shotgun in your own. But there are several short shotguns in the market.
Also, I really want to know in what world you can classify a short barreled rifle as a pistol, and not have an officer laugh at your form before denying the classification and registration. Or classifying a sawn off shotgun as a “firearm”
The automation is because it’s always been a felony not to register, same as it is in virtually every country with mandatory service, so to avoid the horrifically needless societal effects that come from giving someone a felony for a random crime, they simply automated it.
Basically what they did with social security years ago. Used to also be a crime to not sign up by a certain age, so they just started immediately registering all children at birth.