Trivial counterexample: I can't make an Apple M1 chip in my garage. I can't make (good?) LSD in my garage. I can put a metal pipe on a board with a nail and have a simple, reliable 12ga shotgun. I can 3d print a 22LR pistol, or even a 9mm subgun (just add pipe for barrel, weight for bolt, and some common springs).
I assume your response was probably born out of some political frustration, and I respect that. Happy to discuss specifics of the this position on the practicality and effectiveness of gun bans.