its true that localisation of damage is harder underground, but they are a lot less exposed to get damaged in the first place. no exposure to weather and strong shifts in temperature helps quite a lot.  i doubt the soviets weren't able to produce quality pipping... they could produce million of gun barrels... if you can produce gun barrels you can produce quality pipes, the production process is the same up until to a certain point.  maybe its because many of those cities/towns are on steps that freeze over in winter and turn to more or less swamps in summer, and burrowing something there is a lot more effort then putting in over ground.
Austria