THE-QS ranking uses six indicators: academic peer review; employer
review; faculty to student ratio; citations per faculty member;
proportion of faculty that are international; and proportion of students
that are international.
Times Higher Education World University Rankings. The performance indicators are grouped into:
Teaching (the learning environment)
Research (volume, income and reputation)
Citations (research influence)
That’s the explanation why so many highly ranked Universities (top 500) are in English speaking or well to do countries. Many international students go to study to USA, UK, Canada, Australia, NZ hoping to find a job after graduation and settled in these countries. MS programs are popular among international students. Two years of study in the country and your education is recognised by employers. Then an easier way to immigration.
The other reason I already mentioned – most research is done by scholars working in Universities in many countries, whereas in the case of Russia, Belarus, Ukraine research that is peer-reviewed by scholars is done in research institutes.