Countermeasures ARE doctrine controlled, and aircraft do use them with frequency when they identify incoming missiles.
The reason most times that AI aircraft don't drop against incoming IR guided missiles is that they don't identify and classify them in time, which is more or less the case for aircraft in real life... as the only time you would have a warning of an incoming IR missile (except for experimental or new technology as far as I know) is if the pilot or a crewmember actually saw the missile coming towards the plane or helo.
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LW
 
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