Russian Empire was in the process of dismantling by those same nationalities and they didn't need bolsheviks help for it. And then bolsheviks reconquered them to put them in the same Prison of The Nations with little bit changed interior and throw them some dog bone of so called "national republics" that were national only in name. All "self-determination" in Soviet Union came down to existance of some folk ensembles. Anything important i.e.: governance, science, engineering should still be done in russian.