think about this...

[BOTW]

A plane is stuck to the ground cuz gravity is pushing down on it.
To lift the plane, we need airspeed.
There is no wind so airspeed = ground speed.
To get ground speed, we need to move forward compared to the ground.
We apply thrust to the plane.
Relative to the wheels contact on the conveyor, the plane moves forward, so the wheels start spinning.
However, our conveyor spins beneath our wheels at the exact speed our wheels turn.
Hence, if the conveyor itself isn't moving, the plane isn't moving and we have no ground speed.