> Why would I bother with an unreliable 3D printed zip gun and 3D printing when I can go and get a real working gun off the street for a few hundred?

Even in countries with strict gun control, like the UK, the most serious criminals can get hold of guns. And if lesser criminals 3D printed a gun, they'd struggle to get hold of ammo for it. So they stick to knives.

Reading up on this, the remaining UK incidents seem to involve mostly "converted blank-firing copies", with the NCA describing 3D printed firearms as "low status". And as you say ammo is highly controlled here.