I get the sense that a federated image hosting/sharing system would be counter to their goals, that being to lock away their art from AI trainers. An AI trainer could just federate with them and they'd be sending their images over on a silver platter.
Of course, any site that's visible to humans is also visible to AIs in training, so it's not really any worse than their current arrangement. But I don't think they want to hear that either.