Just very simple logic,
@Deino -- in addition to the info posted by
@Temstar and others.
Russian force won't destroy any asset in Ukraine unnecessarily -- unless those assets can be used for the battle benefits of the Zelensky side!
WHY? Because at the end Russia will own Ukraine! And any damage there will be at Russian expense to repair, rebuild in future. This is just a battle to clean up that land from extremist Ukro forces (Azov/Aidar, Right Sectors, etc) and the installed puppet government from the 2014 coup.
Denazification and Demilitarization of Ukraine. Well, Ukraine is Kievan-Rus -- Russia won't destroy Ukraine unnecessarily -- just like China won't destroy Taiwan Island unnecessarily in any future attempt -- understandably both won't destroy their properties unnecessarily -- what's the point to retake in complete ruins. Quite different from the bombing of Yugoslavia in 1999 and Iraq in 2003 for instance. The place of Soviet legacy aircraft is under Russian control, so the only possibility is Ukrainian force destroyed it so Russia cannot have it.