Modern warfare is sneaky. What's the worst you can do without starting an actual war? Plus what's the point of retaliating if the actual combatant was just "an insane person from another country". IE - There's no way to prove he's working for the CCP or IRGC, for example, maybe he's just a crazy person.

Why bomb something, which carries its own risk profile and success criteria, when you can make some piece of equipment malfunction just enough to wear out in a year instead of 20 years?

Unless you're running out of munitions.

And nuclear isn't exactly a great option.