Why is Russia's north-south traffic underdeveloped?

Russia has a vast territory, with a longitude difference of 164 degrees between the east and the west. The population, city, industry, politics and culture centers are concentrated in the west, and Siberia in the east is sparsely populated and rich in resources. The two regions are highly complementary economically, so the economic ties between the east and the west are close, and the transportation mode is mainly railway. However, there are great differences in topography and climatic conditions between the north and the south, the ice period of the river is long, the shipping utilization value is small, and the economic ties between the north and the south are few, so the traffic between the north and the south is underdeveloped.