Explanation:
The Russian Far East wasn't connected to the rest of Russia by roads until early 20th century when the Transcontinental Railroad was completed. Until then, you either had to travel by ship around the entire Eurasia or go by horse drawn sleds in winter - either way the journey would take many months. So the distance itself proved a major hindrance to development and settlement of the region.
The Russian's actually a lot of plans and imagination initially. The Amur was sometimes called "the Russian Mississippi" - a river flowing through a fertile valley and riverine traffic connecting the region to the Pacific ocean. In reality, the Amur isn't at all like the Mississippi. It is frozen for at least 5 months of the year, and its delta is very shallow, prohibiting oceangoing ships from entering the river. Even the much more southerly Vladivostok relies on icebreakers to keep its port usable in winter months.
