Jamming and ECW. You can't rely on communications being possible in key moments.
Same can be said about drones though right?
Latency.
Do you actually know that to be true? Speed-of-light delays would be important for pilots based in Montana flying in Iraq, but not if the remote pilot is in the theatre. And if it's not speed of light, it's a solvable problem.
MIT released open source autonomous drone software that could fly through dense forest at ridiculously fast speeds.