> any asshole with a basic understanding of a lathe and undergrad chemistry knowledge could conceivably run a munitions plant

This makes artillery production fundamentally, physically different from nuclear bombs/subs/carriers or fighter jets too. The supply chain is highly distributive. You can choose to have thousands of distributed small factories each churning out artillery shells. They're pretty damn simple, and the materials and machinery input isn't very sophisticated. Contrast with the complexity of a modern aircraft carrier, submarine, fighter jet, or a nuclear weapon. That supply chain is far more vulnerable. So not only is it a lot cheaper, it's also a hell of a lot more durable.