I’m guessing the strain on the spooled end is less and you want the end most likely to detach close to the ground where you might be able to reattach it, vs in the drone where it would fall to the ground and be unfixible.
The drone contains explosives. You really do not want it to come back to you in one piece.
The relay then gets to spend far more of its power budget on the relay-drone segment and has a very low power relay-base segment. Relay drones also perform surveillance while they're on station. Better bandwidth to the base station from a "wired" connection means a higher fidelity feed or potentially additional cameras to cover a wider area.