Defender advantage.
The old military axiom is "The aggressor needs to outnumber the defender by 3:1 in order to achieve success."
Obviously, there are instances when aggressor's had less of numerical advantage (such as the defender's troops being poor quality).
But in an urban setting that ratio becomes even higher.
Russian's moving in column in an area that isn't full of multi-story buildings is your typical suburban area full of housing and one-story structures which are certainly tall enough to high defenders.
It becomes an easy "point & shoot" exercise for the defenders.
The defender's advantage can be overcome to an extent with infantry deployed on both sides of the road looking for possible ambush points.
But the Russian's probably aren't too motivated to leave their amoured personnel carriers in order to try looking around the corners of various building.
