Simple answer is down to cost vs risk!
Risk is low, cost to harden a320 against DEW/EMP is astronomical - so it never happens!!!! hardening that is!
Also be aware that certain specifics may be in breach of some national security agency rules! If you knew how hard a product was, you would also know how big to build your bomb to destroy it!
Microprocessor manufacturers could harden their products but the cost is prohibitavley high. Indeed as microprossor technology advances the physical distance between devices on a cpu/chip decreases the hardness also decreases such that true hardness becomes dificult to achieve!
No civilian design requirement exists so why allow design creep for a whim?
Data security is MUCH more an issue than nuclear hardening!
In terms of bandwith this thread is a waste of space, there are cheaper ways of achieving the demise of any aircraft regardless of type!