Many routes intra-Nordics see a significant drop-off in demand on Saturdays, because a) there’s no weekday business traffic and b) weekending families and friends driving leisure traffic have usually travelled to their destinations on Thursday and Friday and won’t fly home until Sunday.
SAS and Norwegian tend to either reduce capacity on these domestic/Nordic routes and/or switch it to less-than-daily / weekly short haul leisure destinations. Many of SK’s secondary sunshine destinations around the Mediterranean are like this.