The Soviet Air Force (VVS) embraced the idea of strategic bombing in the 1930s, with the Tupolev TB-3 one of the earliest four-engine heavy bombers to enter service in 1932. Experience in the Spanish Civil War showed the utility of close air support and the limitations of city bombing and emphasis of the VVS moved to battlefront aviation, the shift underscored when leading proponents of long-range bombing such as Vasiliy Khripin were executed during the Great Purge of 1937; Andrei Tupolev, designer of the TB-3, was arrested on trumped-up charges and imprisoned. Independent bombing operations were considered a "bourgeois deviation" (Overy, The Bombing War).

When Germany invaded in 1941 the VVS was still in the process of transition, the ubiquitous Il-2 Shturmovik just coming into service and around half of the remaining long range bomber squadrons still equipped with obsolescent TB-3s. A few raids were mounted on Berlin (largely for political reasons) and other distant targets (549 sorties in total, according to Overy, including raids on Ploiești in Romaina and Bulgarian ports) but tactical missions against advancing German forces were the overwhelming priority and production of the Il-2 took precedence. Strategic air power was not entirely overlooked; Tupolev was allowed to design a new heavy bomber, the Pe-8, but only 91 were produced compared to 35,000+ Il-2s.

The people of Romania would vehemently disagree with you as the Romanian oilfields were hit by hundreds of bombers. Finland, Prussia, and Hungary were also bombed very late in the war. But you're question isn't "wrong" the Soviets did drop very few bombs in Strategic bombing compared to the UK and USA. So I will attempt answer why the Soviets didn't focus Strategic Bombing as much as the UK and USA did.

First, the Soviets and Germans learned their "modern" air warfare lessons at the same time and place, the Spanish Civil War. The lessons they took from that was were that airpower when deployed against military targets during a battle is very effective at destroying, disruptint, and demoralizing the enemy. Look up the German Condos Legion. Their air power and bombing terror tactics became immortalized in the painting of Guernica. So the German backed Nationalists having won and Russian backed Spanish Socialists having lost all learned their lesson. Tactical Bombers and Close Air support wins battles. This is why the Soviets AND Germans focused on light and medium bombers and put little effort on using planes strategically. Why do a long and expensive bombing campaign when you can just march in, crush the enemy with your Air supported army, and end the war right there.

Second, the theory behind Strategic Air bombing is threefols: it can be targeted at infrastructure to hamper movement and logistics, a long-term attempt to destroy the opposing industrial capability, or a terror tactic to target civilians to try to get them to sue for peace. The Soviets for the first half of the war were defending their own territory and trying to win back their own territory. Therefore they would be destroying their own occupied infrastructure, blowing up their own occupied industrial centers, and terrorising their own captured civilians which I'm sure you'll agree would have made anyone looking towards a post war world hesitate.

Third is the industrial impossibility of it. Prioritizing long range heavy bombers and their bombs and flight crews when the Germans had complete and total air superiority and the Red Army was having issues being supplied with things as basic as coats and rifles would have been suicide. Even with American industrial help the Soviet economy had many problems supplying its own armed forces. The Soviet air force had been hit hard by the Purge and as a result of inexperienced pilota they broke every record when it comes to losses with over 2000 planes lost in the first week. They needed fighters to protect their men and cities being bombed right now. No one was going to prioritize expensive and slow heavy bombers when at the rate the war was going if fighters weren't put in the air there wasn't going to be a long term.

TLDR:

1. Soviets did have Strategic bombing but it was tiny on comparison to the allies
2. Lessons from the Spanish Civil War taught them to focus on Tactical and Close Air Support bombing.
3. Soviets were in a desperate war for survival and needed to win battles. A slow destruction of their own now German occupied industrial, infrastructure, and population to hinder the German war effort was not the priority. Getting air superiority and tactical bombers was needed immediately. Expensive slow bombers could come later.
4. Soviet industry had issues euiping their infantry and supplying their tanks there was no "extra" industry lying around to make long range bombers and their bombs. They needed lighter aircraft to win air superiority first.

Sources: John Keegan The Second World War this is also the best WW2 book out there period.

David Glantz When Titans Clashed How the Red Army Stopped Hitler

Richard Overy: Russia's War A history of the Soviet Effort

I also have a history degree and have spent way too much time swallowing dust in libraries reading Eastern European and Mediterranean history.