Which they absolutely are doing, but it's difficult to provide public transport anywhere else than the big cities when only about 2% of Norway is inhabited. The price of public transport is not what's keeping people from using it, but the fact that many people live outside the big cities and have to travel to them for work. Depending on where you live, commuting to the city may be very unwieldy. Oslo has been building out more train tracks recently which make travel time much quicker for a lot of people living outside the city.