That's why.
Rather than look at this, I'll look at E. Ukraine.
A lot of statues of Lenin are coming down in places like Khar'kiv and Soviet-era place names are undergoing a second way of de-Sovietization. At the same time, in other places the culture's being re-Sovietized, in speech if not always in action. That, sadly, is the dominant narrative.
There are two perspectives to consider.
The Ukrainian nationalist way: It's good. The USSR was repressive, evil, and murderous. It was responsible for the intentional famine and for forced collectivization that worsened the famine, for political repression and continued the evil, imperialist work of the tsars'. The Russianization program was ethnocentrist and denied the expression of our culture. We must strip society of all reminders of that evil, oppressive, offensive past. It offends us to remind us of that history.
The Russian nationalist way: It's evil. The USSR may have had problems, but it fought German fascist and largely won on its own. It uplifted millions and provided social services for the many, even if it did hurt the rich. The famine was, nonetheless, a real famine, and Russians also died. Why blame us for language shift--it happens all the time. It's the price we pay for speaking a minority language that's different from the regional, more important language, esp. with a more prestigious culture, and we think Russian culture's pretty damned good and it's racist to belittle it. Moreover, now, as in WWII, WWI, fighting the Ottomans and the Catholics and the Horde, the world is against us and we must stand united in strength. That's been Rus', Russia.
Note that the Ukrainians that are "nationalist" often just want Ukrainian language and culture to not be subject to Russian (and often want to protect it); they're also more often going to be vaguely capitalist and more EU, thinking integration with the West is a good thing if only because it protects them from a more local threat--Russia.
The Russians that are nationalist often just want Russian put back where it was--they feel like they've lost something, and that's hard on the old psyche. They also tend to be older, in areas that are less economically well off these days, and rely more on social services and pensions. They're nationalists and also Communists or Communist sympathizers. They also long for days when they got vicarious satisfaction from victories or, every bit as much, resistance to outsiders--whether the Russian empire or the Soviet empire, whether taking Berlin or partisan activities behind German lines.
Both sides are right and both sides only see their own rightness. One side, sadly, is also into ritual humiliation to a greater extent than the other, as recompense for past humiliation still felt and to forestall future humiliation already perceived.
The Russians need to see that their privileges were inappropriate, and Russianization was wrong. That what the USSR did wasn't all good and light and was, at times, truly evil. At the same time, the Ukrainians have to realize that the cities were industrial and educated, due mostly to Russian influence, and the language shift wasn't just forced but also part natural, as was the famine in the '20s and early '30s. The Soviet victory over fascism was every bit as important as the resistance struggle against Communism and "Russianism." Even purely Ukrainian institutions were modelled on Russian ones (or, at times, German ones). More importantly, both sides have to realize that "I'm good, they're bad" is a sucky way to claim the moral high ground or build community or a community. What's left is all-or-nothing warfare. In some ways, since they do share some common accomplishments and culture (it's the post hoc claims of "it was all us" or "it was all you" that grate), this job shouldn't be all that hard. But it is.
If this closeness of the parallel with the US doesn't gobsmack you, I don't know what to say. It's not a question of not seeing the trees for the forest, it's a question of not seeing the trees because those pesky moss leaves keep towering over us and getting in the way.
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