There is a simple reason. Although the current military unmanned vehicle has the function of automatic driving, it can only plan the route according to the established procedures like an unmanned vehicle. Although they can avoid obstacles, they don't have human intuition and can't judge emergencies, let alone predict the situation. However, if the operator relies on remote control, the complex ground environment will seriously interfere with signal transmission (in the air, it is easier to control whether it is direct communication or relay control because of fewer obstacles), which makes remote control difficult. However, if the console is arranged near the battlefield, it is in danger of being attacked (if the front line is maintained, the enemy is not afraid of frontal attack, but it will be difficult for the enemy to attack outside the defense zone, attack with unconventional weapons or sneak attack by special forces). Therefore, large unmanned armored combat vehicles have not been put into practical use (if quantum communication technology can be popularized, then this problem will be solved).