That's because an AK-47 is an AK-47: it's not a game-changer. But a CNC machining system that lets you build silent ship propellers can dramatically change the threats the world faces.
Building a CNC machine with a regular lathe and mill may not be hobbyist level easy, but it's certainly doable by someone as rich in machining tradition as Russia.
Amusingly, the incident would also dispell the (western) myth that it takes very advanced machining technology to build a nuclear bomb. You can't have it both ways.
I suspect the real incident was the software to mill those propellers, but that wasn't on the list of illegal goods. It's one thing to have a fancy but dumb CNC machine, another to come up with a silent prop design.
All the advances in CNC machining systems are published on the internet. And there is some degree of self replicating capability in them (basically you can machine the parts yourself, and fine-tune the design by hand to get a machine of better capability than the previous one).
