So, I was rereading the first comic. Bat City literally has electricity coursing through it. So, I was thinking that desert borns get a narily shock when they first enter the city’s walls. Or they have this overwhelming feel and they don’t know why. Maybe it provides a deafening hum for people who aren’t used to it.
Maybe, kids on both sides wander up to the border. They get shocked, for the BLI kids it enforces a ‘don’t leave the city’ mindset. For the ‘joy kids, it reinforces that the city is dangerous.