Well when you book premium with Norwegian you have to choose your seat, there's no other option. When you do it updates the seat map and blocks the seat off, plus you see the other booked unavailable seats.
so when I fly on the 29th it's just me in the cabin.
Did a mock booking for tomorrow the 20th return 22nd and theirs 9 going and 2 on the return.
So perhaps it's not that unusual.
Was just concerned when I heard that people where denied premium cabin because too few people. First time iv'e done Premium and don't won't to waste my money i'm sure people can understand.
But as you say does seem strange if they don't offer it, should be easier for them.
To be honest I shouldn't complain if I have the whole premium cabin to myself.