The city of Donetsk is at the edge of the front line. The city proper contains the artillery, command, logistics infrastructure, security services, all the “back end” of an army.
Counterbattery fire against Russian artillery could easily endanger civilians. Just one consequence of trying to run a military operation from a large city.
So all those years prior to the war the Ukes were just practicing for when the Russians would show up? Makes sense.