It helps to know that the Titanic was underinsured with the remainder of the risk covered by White Star's in house insurance fund. Nobody is going to perpatrate a fraud where they rook themselves out of what amounts to a third of the ship's value.
The sheer complexity of the whole scenerio is another fatal flaw. For insurance fraud, all you need is the constructive total loss of the vessel and an enterprising young man with a can of petrol and a book of matches can make that happen easily enough.
yes, I heard that theory too once and is certainly not true. To be sure, certain identifying numbers (I believe one was found on the stern section by the overhang---but correct me if I am wrong about that!) that had the actual hull number were evidenced during a dive some years ago that matched Titanic's numbers.