I never said turning off the transponders made it impossible to track the airliners, so I guess your reading comprehension is pretty poor, as is your knowledge of aeronautics and military operations.

A transponder is simply a specialized transmitter that sends a coded 12-bit identifier back to ATC when it detects a radar signal. Almost all transponders also use Mode C encoding to send back altitude info. By themselves, ATC enroute radars only track azimuth, elevation, and range but no altitude info due to their antenna and beam geometry.

The identifier code value is assigned by ATC for a specific flight they're controlling. When the ATC radar receives the identifier code pulse, a computer correlated that specific radar return with the identifier to display flight info on the controller's screen. When the transponder fails or is turned off, all the controller sees is a tiny little blip without any identifier info. It can be very difficult to pick out that blip out of the background clutter and all the other planes. Without the transponder, a plane is damned near invisible on a controller's radar screen.

When a plane suddenly stops sending transponder signals, that in and of itself doesn't mean anything. Like all other electronics, transponders sometimes fail, as do the electrical systems that power them. I had that happen to me during a flight last December. I proceeded to my destination airport, checked very carefully for traffic (fortunately, I had the pattern to myself), and did a no-flaps landing (electric flaps have their drawbacks) without incident. What were they supposed to do, shoot me down because my voltage regulator failed and took out my battery?