It uses laser to track its target. This is not a bright idea for an all-weather system. You don't see through clouds with a laser. The missile tracks the laser beam. There is also the minor problem that the computer system can't tell friend from foe.
Reliability is a problem.
The system is thought to be so complex that its reliability may never reach an acceptable level. Pilots are cautious people. There is a school of thought which believes that complex electronic systems are, or can be made, the answer to everything in modern warfare. For those involved, there is no advantage in cancellation, even if it doesn't work. To get the troops something they can use is at most the third priority.