Cuba is a sovereign country that stole people's private property. U.S. law holds that those docks are the legal property of Havana Docks Corporation and it was illegally seized and used by the Cuban government. Norwegian Cruise Lines used those docks for their business and paid the Cuban government for their use, but the Cuban government doesn't legally own them, Havana Docks Corporation does.
There are a lot of grey areas and politics here. The Cuban revolution was 64 years ago and the communists stole the private property of virtually everyone in Cuba. Most people that has their land/homes/property stolen are dead now. How long do their descendants claims last? Obviously as long as the communists control Cuba they're not going to get their property back. Norwegian Cruise Lines opened themselves up to a lawsuit by doing trade when we had an embargo in place. Norway might not have a beef with Cuba but the U.S. has long had sanctions in place against them and Norway does business with the U.S. The U.S. has a long history of using our legal system to go after other countries monetarily when they go against our wishes. Is it right? I dunno, it's kind of being the bully and throwing your weight around on one hand, on the other hand if you don't enforce your sanctions against Cuba they're just going to end run them like Iran constantly tries to do with oil.
I would hate to have to pay reparations for all the property the US has stolen directly or by proxy.