Hello Mathias,
There are so many requests about ships. Simpley VSTEP makes the choice which ship will, and which won't be added in ship simulator.
So answering your question why there are not any Norwegian ferries in SSE, is VSTEP has not decided to add it in SSE.
You can always put a request in the special made forum, but as Dexter said there are already 8 ferries in SSE. So I don't give you much of a chance. Or hope there comes a second CCC, and make one yourself.. But don't know or you any skills with 3d modelling.
Jajaja kunne godt tenkt meg Boknafjord
Would be polite to keep it in English for everyone.
Snaky