I'm not sure what type of electronic defences you have in mind but if it's jammers I assume that it's a lot easier to deploy those in the relatively quiet, well

I'm not sure what type of electronic defences you have in mind but if it's jammers I assume that it's a lot easier to deploy those in the relatively quiet, well bounded and controlled environment of a prison and much more difficult in a very large airport hosting thousands of people and companies using thousands of devices. I think people want their cell phones and wi-fi to work correctly within the airport. And of course you don't want to risk messing with the electronics inside the planes. If you play the thought experiment of "how could somebody kill many people easily and without requiring a lot of money" unfortunately you'll find that it's pretty damn easy. You have to find a balance between avoiding attacks and preserving freedom.