I think we have a lot of people having very different discussions about what "3D printed gun" means. This can be anything from a fully plastic weapon like the Liberator to what you're describing (more 3D components and home assembled traditional components coming together which really just feels like the "80% receiver" style ghost guns) to a fully metal 3D printed 1911 off a machine that itself costs at least half a million dollars to acquire.
Point being: Yes they do, but also no they don't, because you're having different conversations about different types of weapons. Are fully plastic weapons commonly used for anything? Doesn't seem to be, and I would suspect the reason is because they'd be inclined to blow up/warp after a single fire.