It's not just good PR for politicians to pass "<specific instance> case of already illegal <generic> is explicitly illegal"-laws. Prosecuting a violation of <generic> tends to be a lot harder because in addition to providing evidence for <specific instance> it requires convincing a judge that <generic> even applies to <specific instance> in the first place. You get to short-circuit that ordeal by passing a law that clarifies the intent that yes, <specific instance> is in fact an instance of <generic> without having to go all the way through setting precedent in higher courts.