In many cases, these are public or quasi-public works, and security is a cooperative venture between the engineers who develop vulnerable structures and the state. Rather than building bridges to withstand artillery strikes, the nation itself implements national anti-missile defense making it quite difficult to launch an artillery strike, and if one gets through, they strike back.

I'm not really sure how to analogize this with software. The reality is some communications networks were just never meant to be secure. This isn't unique to the Internet. Nothing ever stopped anyone from tapping your phone and stealing your personal information that way except that it is illegal. On the other hand, a whole lot technical measures are in place to make sure it is very difficult and maybe impossible to "tap" a military or classified communications network at all. Nobody can stop you from intercepting radio, but good luck breaking the encryption.

But the national security infrastructure can't extend that level of protection to everyone, just as average citizens don't get police escorts and personal bodyguards assigned from the secret service. If someone wants to shoot you, the only thing the state does to stop them is make it illegal. Otherwise, it's on you to protect yourself, and we don't hold clothing manufacturers liable for not making your t-shirt bulletproof.