First and foremost, drones are both cheap and unmanned.

Second, drones can cover a *much* greater distance much more quickly (with much less risk) than can, say, infantry or armored vehicles with TOW launchers.

Third, there's the matter of morale, not only in the tank crews (who know that they are slow-moving, easy-to-hit targets) but even among the leadership, who know not only that tanks and infantry columns are quite vulnerable but also that each tank represents a much greater economic investment than do cheap, unmanned drones.