I think the question is phrased wrong. It would be smarter to ask why are western Europeans so tolerant - the answer is we have a colonial history. Russian colonial expansion was the subjection of neighbouring ethnic groups whilst British people have ruled and had close contact with "ethnics" for nearly 500 years.
If you visit many parts of the world, the Russian/Eastern European approach to foreigners tends to be the norm. It is the west that is exceptional in its tolerance.