Just watched a video of someone assembling a look-a-like Glock it said all that was required was a Dremel, a few Swiss files, and a couple of screwdrivers. Mostly these are required to remove 'tabs' that are intentionally left in place to stop the 'slide' working so not exactly an onerous operation. And bingo you have an unmarked weapon (as long as you pay in cash!)
You don't have to pay in cash. It's legal. It's also not cheap and while your video may have made it look easy, like any hobby, you have to learn to do it properly. Unlike other hobbies, doing it improperly can have pretty dire consequences.
Again, why would a criminal do something expensive and time-consuming AND requiring some skill when they can buy a gun on the street faster and cheaper.
Pass laws, or enforce laws, those impact criminals, not legal weapons owners and hobbyists.