Let’s try to reframe this question, as to why the East Slavs and others in the Russian empire didn’t develop separate nationalist movements in the same way the South Slavs, Romanians, and Greeks revolted against the Ottomans?

Well, they actually did! Let’s start with Russia in 1917, as the Russian Revolution is beginning. Finland looks to independence, The Baltic Republics (Estonia, Latvia, and Lithuania) are also overthrowing the Russian empire. The Poles, never happy to be part of the Russian Empire, rose up as well.

The Russian Civil War breaks out in the aftermath of the Bolshevik Revolution, and while the White Russians (the anti-communist faction) is defeated, anti-Bolshevik, pro independence forces in Finland, Poland (including parts of modern Belarus and Ukraine), and the Baltic’s all are able to claim victory. While separatists in the south Caucasus, in Armenia, Georgia, and Azerbaijan, are defeated by the Soviet Army, as well as the separatists in Belarus, Bessarabia and Ukraine.

The Russian Empire collapsed, but what replaced it was not a nationalist movement, but an idealogical based state. Soviet ideology was based on class, not ethnicity, and focused distinctly on the economic nature of the state and the internationalism of socialism. “Soviet Patriotism” was not a “nationalist” sense of loyalty, because such nationalism was a product of the “bourgeois” capitalist class.

Ethnic nationalism abounded in Eastern Europe as much as it did the Balkans, and elsewhere at the turn of the 20th century. However, many of the movements failed, and the idealogical aspect of the Russian civil war meant that there were infighting even within the nascent states (for instance the largely concurrent Finnish civil war was fought between Finnish Communists and Finnish Nationalists). This often allowed the Soviet army to simply absorb the local communist movements into the Soviet Union.

I’ll add sources in a trailing comment