Because if you classified as supply chain risk, ANYONE who does business with DoD/DoW cannot use your product in any capacity.
Looking at it by top 10 US companies by revenue, Walmart, Berkshire are probably only two that MIGHT not have DoD contracts. Amazon/Apple/Alphabet do for sure. CVS/UnitedHealth probably supply DoD healthcare, Chevron/ExxonMobil very likely supply fuel and Verizon supplies telecom links.
So if you are Anthropic, those 8 companies cannot use your software AT ALL. That's massive potential revenue to lose.
On the contrary, they are free to use it outside the defense supply chain.