I think it was because Stalin championed the cause of Russian nationalism. Also, Stalin's system of feudal serfdom was slightly better than that run by the czar, and this gained him the support of the Russian masses. Everyone was willing to make allowances for him.
我認為是史達林提出了「大俄羅斯」主義，以及在史達林主政下，比起沙皇好一些的農奴封建統治制度，讓俄國的老百姓折服了，因此大家遷就他。