Battery degradation, a year or two's worth of leaves and debris accumulating on and around the drones, literally all of the elements affecting them, animals, etc.
If I've gone to the hassle of setting up a high tech bombing attack, wouldn't I have also gone to the trouble of putting the drone in a self-opening container?
This no longer sounds cheap or relatively straight forward, it sounds more like an engineering challenge the requires technical expertise and skill to pull off, as well as considerable amounts of money.
Battery degradation, a year or two's worth of leaves and debris accumulating on and around the drones, literally all of the elements affecting them, animals, etc.