I grew up in Norway. The way I see it is that weekends are for spoiling yourself with the most delicious food. Another common tradition would be making pizza on weekends. Taco Friday is seen as a special weekend treat.

I know taco and pizza aren't really that special or fancy meals, but I guess they turned out that way in Norway since they came from abroad. They're still not seen as "fancy", but they are many people's favorite tastiest food.