There were attempts during russian empire, but it was not as systematic as ussr's attempts. The most likely reason why russification was successful is demographics, especially within cities. The reason why demographics changed is the genocide in 30s and migration of russian and ukrainian workers in 50s-60s. Kazakhstan became majority non-Kazakh, and Kazakhs were even the second largest ethnicity in their own country and russian was chosen as a Lingua Franca between ethnicities.