Complexity and reliability. If the batteries die on your xbox control mid-Halo, it's just annoying. If the batteries die on your remote machine gun with the enemy literally at the gates, it's life and death.
I don't think there's much need for wireless inside the tank in any case. Maybe for a remote placement turret without a vehicle mount it would be more useful.
I actually meant wireless so that you wouldn't have to be present inside the tank, you would control the gun remotely.
You would still use wired controllers, but you would use wireless networking to control the tank close by. As long as you maintain a connection with the tank, you are safe from enemy fire, and the enemy would be shooting at an empty tank, with no way of telling what your physical location is.
Even more increased complexity. That would require them to make electronic controls for the steering, gas and whatnot. More parts would thus be required.
In addition such a system is highly prone to jamming considering the kind of parts they have available, and the location of the controlling transmitter can be quite easily triangulated.
Just wanted to point out that it's not so easy to make a wirelessly controlled tank and the benefits can be dubious.
I don't think there's much need for wireless inside the tank in any case. Maybe for a remote placement turret without a vehicle mount it would be more useful.