If you bought a BMW in the 80s and you were suddenly at war with Germany, you'd be stuck scavenging for replacement parts the moment something in the engine failed. It's not as easy and direct, but the problem is still there.

Doing business with the enemy always comes with a risk. For countries that don't build their own networking equipment (including the PCBs and chips), you have to accept some level of risk or you have to avoid such technology all together.