>Почему Армия России отступила...
As reply to all such question:
Perhaps Russians could only get supplies and reinforcement from the west so giving up land for shortening the supply line was a good trade. In return they could hope that lengthening the Japanese route will impose problems for the enemy.
Also should note that this war wasn't like WWI with the lines of parallel trenches where retreat was just a couple dozen meters to the line back. A beaten, disorganized army had to regroup somewhere, and couldn't just take a step back and wait.
What you guys think?