Because the TOW is a wire guided system, optically tracked. It derives its control signals from the wire. But still, its rated range and flight time at range is 6 seconds short of what the story mentions.
The next question would be just how long the fuel lasts. If it runs out of fuel at that same point, what would the velocity loss be and what would that effect have on any penetration performance?
Shape charge penetration doesn’t rely on the delivery vehicles delivery speed / velocity. But accuracy does. Velocity / Penetration not the issue at the end of the weapons range in this case..... accuracy is. If it gets there it is gonna kill if it hits, even if its a free throw from full court shot.