The primary reason it doesn't happen is because it's a lot harder to pull these things off than the public perceives. The examples of supply chain attacks in t

The primary reason it doesn't happen is because it's a lot harder to pull these things off than the public perceives. The examples of supply chain attacks in the wild, or within some controlled environment discussed ad nausea in conference settings are completely different than a supply chain attack against a nation-state with sophisticated intelligence and counter-intelligence agencies. It's not even worth comparing them. The consequences for making a mistake in a supply chain attack against a nation-state are extremely grave, i.e., expect torture and execution in your future. Imagine arriving in a foreign country and trying to gather the information needed to pull this off. How long before someone finds your behavior peculiar and reports it to the state for investigation. Now you have to accomplish your task knowing there's a good chance you're being watched closely.