Even in my lifetime - I'm 44 - the growth in wealth in Norway has been astounding.
Ironically, for example, whale meat is something I remember from my childhood as a cheap meat substitute (but that is now an expensive "delicacy"; we never saw it as a delicacy then - it is tough and oily) because my parents despite both having good jobs could not often afford beef in the early 80s. Even then we'd usually have it only once a week.
When I was a kid, a packed lunch was an economic necessity for many families.
This was also in some sense exacerbated by more income equality: eating out is relatively expensive in Norway because serving staff are also paid reasonably well.
But I think the main reason the matpakke has survived is basically that this was much closer to the norm a lot of places with low population density (~13 per square kilometer in Norway) berfore urbanization and well into early industrialisation and that Norway also for a long time was very severely lutheran, with a puritan streak. Even if you have money, showing it off is not the done thing.