It's still odd that there are no ferries between Scotland and Norway, given the historical connection between the two countries. It wasn't that long ago that you could at least get from Newcastle (at least close to Scotland) to Bergen by boat.
Cost of fuel went up.
J
Not just that, there's also the cost of retrofitting emissions control on older ferries in international service; in many cases they had to be replaced completely.
The cost of doing that for a marginal service is prohibitive.
Scotlands links to Norway don't amount to much; even the Shetlanders don't have a pressing need such that Smyril line reduced their Denmark-Norway-Shetland-Faroes-Iceland service to just Denmark-Faroe-Iceland; the berthing costs at Bergen and Lerwick were more than the extra traffic; they tried Scrabster for a bit too but no different.
Unfortunately if you're going to Norway it's just too easy and cheap to hop on a plane at Aberdeen and be there in an hour rather than a potentially uncomfortable 12 hours; and if you're doing that you're likely either going on holiday or working for one of the oil companies that operate in both sectors.