Stand off assets, like AWACS for example, are often squawking as they may be in adjacent airspace which may not necessarily be military controlled, so they will be displayed quite openly on a civilian based radar syetem (as was the case in this theatre) and therefore be readily observed by enemy based systems.
The mushroom on top will also be pumping out a lot of energy! The ac could always shut down the radar and allow the enemy to notch up a soft kill...
I recall the threat of long range and high ceiling SAMs being discussed as a potential source of worry to the men and women at 30,000+ feet.