In the phrase “security through obscurity”, obscurity means obscuring how the system works, eg making the source code secret. Mac being less popular has nothing to do with security through obscurity. The argument is that a less deployed platform is a less valuable target, which is absolutely true.
That’s hilarious, assuming they only regulate prebuilts or full kits, all you’d need to do is something like add everything from a voron parts list to your cart to get around it. I wonder if sellers would also be able to offer partial kits to bypass it too (like offering a frame kit, x axis kit, extruder kit, etc and you just add all to cart)