And it shouldn't be Apple's problem. Apple is not a court of law. They have no business knowing about their developers internal affairs, imagine the conflicts of interest. This is a matter for an actual court of law, that can issue warrants and subpoenas, where perjury is a thing, where there is fair trail and where you can ask damage and the guilty party get charged for fraud. You obviously don't want to give these powers to a private company.
But yea, if you're a business that makes money promoting other people's content then you're responsible for that content. Similarly, I'd argue that a skywriting company that writes libel in the sky should be held responsible as an accessory to the client if they were aware the statements were libelous.