Why should a United States court have jurisdiction of a shipwreck in international waters?
The short answer is that it’s insanely complicated. It’s all bound up in questions of maritime law, specifically salvage law, who owns the wreck, what rights the insurers had and who those rights passed to (the ship was British built and registered but the White Star Line was owned by an American shipping conglomerate) and then there are laws passed by various countries limiting what could be removed from the wreck site. And so on...
Limited jurisdiction per international agreements. Do you know how to Google?