Good question Todd.
Right now Cunard is the only cruise line that has somewhat of a transatlantic service on the QM2.
I do believe that if there was money in it for the cruise lines they would jump on it like a cat on a mouse, or me on a New York steak.
I think one of the biggest deterrents for this is one of the same reasons why the cost of airfare is so high. The cost of fuel. Having a repositioning is fine but I believe the cruise lines make little or no money on the fares for these cruises. They make their money when they get to their destination. The Caribbean, Europe, Asia or wherever.
I do believe that if they could make money of them they would but I don't think there is money to be made in transatlantic cruises.