You pretty much need to be a gunsmith to create a reliable weapon that won't jam and won't explode in your face. In most countries you can't order weapon parts online - all load-bearing parts are regulated. You can't manufacture those without gunsmithing skills and equipment.

This is why criminals prefer to smuggle industrially manufactured illegal guns from somewhere else instead of making them at home.

Gun laws don't prevent someone from making shitty homemade guns. They prevent them from getting properly made ones. Accessing gun smuggling networks isn't that easy without connections to the criminal underworld.

I looked up Luty's homemade firearms. He claimed that they can be manufactured by anyone. But that's obviously not true. He definitely had good metalworking skills. I certainly would not be able to manufacture anything like that at home.