You obviously haven't thought this through.
The same thought occurred to me, but I discarded it after about a nanosecond of deep concentration and reflection.
What if the drone, due to a malfunction, falls on your territory, and is recovered by your allies, by civilians, by neutral parties, or even by your own troops who don't know its been secretly booby-trapped? What if it crashes and burns on landing or takeoff in one of your own bases? What if the bomb malfunctions, and either goes off prematurely or fails to go off when required? What if the hangar or ship where it is stored is hit by enemy fire and the drone is set ablaze?
You can't solve every problem in the world by blowing it up. "BAM!", my ass.