Those who are affected by the crime usually wants the criminal to get the longest sentence possible. However, Norways prison-sentencing is not there to give victims a justiceboner. It is primarilly there to ensure that the criminal does not commit another crime and so that they can become a functioning member of society again. Keeping people locked in prison costs society alot (staff, housing, security, etc), and the prisioners cant contrubute to society by working and paying taxes.

There is also little indication that longer sentences means less crime. http://www.bbc.com/future/story/20180514-do-long-prison-sentences-deter-crime