It was a probably a combo of things, but the images of Ukrainians tearing down statues of Lenin right after the winter Olympics (in Russia!) has to be near the top.
The 100th anniversary of the Russian October revolution just passed, with minimal and lukewarm remembrance from the official state. BBC ran a whole series of segments on this, interviewing school children and ordinary Russians and state officials -- knowledge of the 1917 Revolution was thin.
Stalin, different story, because he fits into the 'Great Russian' nationalist narrative -- and was the leader during the Great Patriotic War.
Dead wrong.
Stalin is remembered first and foremost for the great purge of 1937, inducing famine in Ukraine and displacing people en masse. His most notable "contribution" to WW2 was his complete silence during the first few days that followed June 22nd. He abandoned his duties as the supreme commander at the moment when he was needed the most. In my age group it is generally accepted that WW2 was won by generals and marshals despite Stalin being at the helm rather than because of it. Stalin is remembered for his cruelty and cowardice, not his leadership.
Take a look at https://www.rt.com/politics/394158-russians-name-stalin-most...
That's in other countries. In Russia he is remembered for WW2. Official narrative is something like "yep, he killed some people and was wrong sometimes, but they were reabilitated some 30-50 years after, so what's up", BUT he won WW2.