From time to time pilots not use flares. Mostly when he's in close range with AA spec (like in 200 meters).

Also AA specs can see helis from 1-1.5km range or more and shoot rockets from this distance. AI pilot react on this with flares (counter measures). But he react from the start of rocket flying. So when he flares, rocket in range when it's not affected by flares. And to make another flares volley pilot needs some time and he becomes hit by AA rocket.