Thank you and I wish you luck with your plans.
Let's put it into perspective;
Norway has around 5 million tourists annually whereas Greece has 22 million, Germany 33 million and Italy 50 million, and these 3 countries have smaller areas than Norway.
High costs (Norway being one of the most expensive countries in the world) and short summers are obvious reasons.
Tourism is definitely picking up in Norway due to its sublime natural beauty and given that the Norwegians are a very outdoorsy people.