They take that into account and have even done randomized trials. DARE unequivocally increases drug use. The primary reason (although there are many) is thought to be that because the information is unreliable and sensationalized, kids learn that anti-drug information is wrong and therefore see little danger with using drugs and may even misunderstand key drug concepts like addiction. This is true with a lot of the commercials, too. But those often aren't really funded with any real intention of affecting drug use, it just makes politicians look like they're doing something constructive.