Why does a turbofan shut off when rapidly retarding the thrust levers? In a turbofan engine, when the thrust lever is at maximum and is then suddenly pulled back to idle, the engine will shut off and lose power.

How can this be the case as the engine should be at idle when the thrust lever is brought to idle? But in this case, the engine shuts off because of the sudden movement. What is the specific reason for this?
The rotational inertia of the fan will continue to push air through the engine after the fuel supply has been reduced. Reduce the fuel supply too quickly and the result is like holding a match in a gale: the wind blows the flame out.

To prevent this, modern engines use digital controls (FADEC) to ensure that the engine is kept within its operating parameters regardless of what the pilot might do with the throttle.