The fog was being lifted, but the truth coming to light was unbearable for some. That combined with the societal instability of the 1990s following the Soviet collapse...made for reluctance to dredge up the past.
Then of course: Putin came along. He put a lid on the whole thing. No more discussion to be had. (Well maybe an occasional memorial or two...)
But the millions enslaved, imprisoned, tortured, and slaughtered are not to outshine the “victors.” Today, Stalin is considered a hero by most Russians.