Most drone cameras use the rolling shutter technique because it is less expensive to build from what I have read. I don't know the technical aspects to know why it is more expensive to build a global shutter sensor.
So what does this mean for the drone mapping world?
With todays digital cameras the speed at which the image is stored is extremely fast which has little affect when flying at slow speeds which can be controlled with rotor wing drones.
Flying at faster speeds such as fixed wing drones does require a more expensive camera and global shutter technique to get good imagery for mapping. This is why fixed wing drones cost more than rotor wing drones.