The reason you don't understand this is because you are ignorant (perhaps willingly so) of how the people that want to ban weapons have thought out their plan. These people know that banning handguns, or most any weapon really, is the goal but they also know that banning handguns is difficult politically.
To understand this best we must go back in time by nearly a century. The National Firearms Act of 1934 placed a prohibitively high tax on a number of weapons, among them were machine guns, firearm report suppressors ("silencers"), "destructive devices" (grenades, landmines, large bore ammunition, etc.), the curious catch-all "any other weapon", and the also curious "short barreled" rifles and shotguns.
Let's talk about that "short barrel" category. The 1934 NFA originally had the intent to ban handguns and to prevent people from making handgun analogs from the not banned rifles and shotguns they made sure that people would not be allowed to shorten the barrels on these "long guns". Because of resistance from a number of powerful groups the ban on handguns went away but the "short barrel" designation remained. This law created the distinction among "handguns", "long guns", and "short barrel" arms where none existed before.
Forty years later the group Handgun Control Incorporated was created, with the (obvious) intent to ban handguns. Again this was met with resistance politically, few people in politics wanted to be associated with a group of that name. In 1981 James Brady was seriously injured in the assassination attempt on Ronald Reagan. HCI found themselves a new "mascot" and renamed themselves to the Brady Campaign. James Brady was shot with a .22 caliber revolver, which seems like a perfect mascot for an organization that wanted to ban handguns.
At about 1989 HCI renamed themselves Brady Campaign but still kept their original intent on banning handguns. The difference now is that they didn't wear this intent on their sleeves. It was now more politically acceptable to be an advocate for those injured by "gun violence" in general, leaving out that the ultimate goal is still banning handguns if not all firearms.
As the decades passed the banning of handguns became even less politically viable. People wanted personal defense weapons and a handgun makes a reasonable weapon for this task. The people today that call for "reasonable" gun control can draw a direct lineage to those people that wanted to ban handguns nearly a century ago. Given the age of many of these politicians and public figures I have to wonder if these aren't the same people that signed the 1934 National Firearms Act into law.
These bans on "assault weapons", magazine limitations, and background checks are all part of the boiling the frog, oiling up that slippery slope, or what have you that will lead us to banning handguns. These people have tried for over a century now to ban handguns but the majority of the people won't have it. They are still working on sharpening the point of the wedge between people and their personal defense arms. They think that by creating the idea that limits on some arms should bring us down the path to limits on all arms. That once we create the idea that the government should be able to dictate with what tools we are permitted to defend ourselves that at some future point in time the government would be able to dictate that the people cannot have any tools of self defense.
This has been going on for a long time in the USA, the best that they've been able to do is place some rather trivial limits on the people's ability to arm themselves. What I find interesting about these advancements in 3D printing is that it makes all those laws irrelevant. They can make it illegal to manufacture these weapons but the people that feel the government should not be able to dictate how the people may arm themselves will find these bans exceedingly difficult to enforce.
This is a question I've asked myself many times, is a law really a law if the government lacks the willingness or ability to enforce it? Congress can pass a law dictating the color of the sky but that does not make the sky any color other than blue. Look at the federal marijuana prohibition and the number of states that have openly defied the ban. Marijuana is not prohibited any more because the government lacks the will and/or ability to enforce it. If people can make machine guns in their basement with nothing more than a $1000 printer, melted down Coke bottles and beer cans, and some files they downloaded from the internet then does a ban on machine guns really exist any more?
Remember folks, people in the USA used to be able to mail order a Thompson sub-machine gun from the Sears catalog less than 100 years ago. Civilization didn't end then. If this ability is restored by technology, not legislation, in 2034 then I expect nothing real to come of it other than people regaining a freedom lost 100 years ago.