But now you've forced your adversary to deploy and use "this little guy" on top of everything else they're doing. If you raise the costs high enough that they can't pay, you win. Yay!

the operator of those would get hit by an aerial drone from one of the other tunnel exits

a network of tunnels and sensors is easier to defend than a open space exposed position where drones can see you from miles away, I guess that makes tunnels better for defense