Even for those, you can get 80% finished parts for those - just drill a few holes, and file off some tidbits, and you get an almost factory-spec gun.
I'm no expert on US gun law, but afaik, some states even allow you to make your own guns without registration, as the law defines gun manufacturing as manufacturing with the intent of selling them.
So there's plenty of options, many of them better than making a gun with a printer.
But even all this is typically overkill, I dont think criminals go to these lengths to make their own guns, they just get them from somewhere.
this hasn't been true for like 5 years now
But even then it's not that difficult, it's entirely possible and legal in many states to print a polymer lower for a AR15 or Glock 17. Then go buy a parts kit from PSA $450 and have fun zero background check or sales tax required as the smaller gun parts stores do not have multistate business nexuses.
It is also not difficult to 3dprint a glock switch, even though they illegal per the NFA https://3dgo.app/models/makerworld/2035005.
This is 100% virtue-signaling from politicians.