Why was the study of the territory of the Far East in the 17-18 centuries much difficult?

The reasons for the belated and slow study of the Far East can be considered its remoteness from the European part of Russia, and it was from there that the explorers went to the Pacific Ocean. Secondly, until the end of the 19th century, there was no railway to the Far East. And the Treaty of Nerchinsk with China of 1689 also influenced, according to which Russia did not master the territories east of Dauria (that is, east of Chita).