Speculating at a 10,000 foot view: It may just be the case that, in any real conflict, phones, the internet, etc. are doomed no matter what. It would be so easy to cripple digital infrastructure with physical means it probably doesn't make much sense investing in digital prevention.

Physical safeguards are both easier to implement, easier to demonstrate when funding is decided, and generally the better investment considering most compromises of government digital infrastructure come from people with direct physical access (plugging in a dropped USB, spies, phishing, etc.).