Drones fly pretty high and usually avoid contact with the enemy, and if there's trouble, they can easily flee and come back later. For on-the-ground vehicle, one need to stay much closer to the enemy, and if something goes wrong, the opportunities for fleeing are much harder to come by. You certainly don't need to physically be on top of the tank to jam - there are military systems that can disrupt communications in a wide area. And, probably, just dumping something non-transparent on whatever it uses to acquire visual information would work too. There would be nobody to come out and clean it up - a trivial task for a human, much harder for the robotic drone. Humans are very flexible, robots aren't, at least not until we get some AI going. And tbh, if we have such an AI, I'm not sure we really want to give it a tank to drive around.