Why are there no American cruise ships?

Ships registered in the US must use American union crew members, and their higher pay rates. It is also why all cruise lines touch some foreign port when cruising from US ports. If they don't they must use union workers. The only recent exception was inter- island Hawaii cruises, I think there was an attempt to keep it within the Islands. Although in the past all Hawaii cruises went to Fanning (Christmas) island to avoid the US only rule. Found out that NCL does operate cruise ship in just the Hawaiian Islands. The crew must be 90% U.S. Citizen.