Why did the first Russian explorers go exactly to the north and east? Why not another one?

The main reason that the first Russian explorers went to the North and East of the continent is the fact that by the time the great geographical discoveries began, as well as the active development of Siberia, all other territories of the continent had already been explored.
There were a large number of trade routes with the West and the South, as a result of which a large amount of facts and information about these regions had already been obtained, while the vast territory located beyond the Urals and in the Far North remained a mystery to most.