It's because there are always gullible people who can't find or afford bud, who haven't heard that the "legal weed" doesn't do anything. The ads make it sound like the buds are going to get you really fucked up and the desperate stoner thinks he has finally found a way to get high. It's just too appealing an offer. And who is courageous enough to sue these people for false advertisement? Who wants to stand up in front of a judge and say "This fake marijuana didn't get me high like the ad says"? It's an industry that relies on a constant influx of desperate (usually teenage) stoners since they get almost no repeat business.