The difference is in who they are selling the product to. The iPhone has a very broad audience, some of whom may want to do photography with very little understanding of the field. They see the product. They see the results. They don't see the context. Someone buying an A7iv probably has a stronger understanding of the field to start with. They are likely looking for a specific product for a specific reason. If they don't or aren't, they almost certainly would have a better idea of what they are getting into by the time they actually make the purchase. (Perhaps through their own research, if not the up-sell would clue them in).
