The established tradition of bringing a homemade meal packed in a bag means that nobody has really been clamouring for cafeteria service -- everyone has simply accepted that schools don't provide food, and so people don't look to schools to provide a service that they don't view as being part of the school system.

Better income equality also means that everyone can afford to provide their own lunches.

Note that some Norwegian schools, especially bigger ones in the larger cities, now provide hot lunches, but the practice is fairly new and still uncommon.

(Source: Am Norwegian.)