In centuries past, the majority population of various cities in Eastern Europe consisted of people from Western Europe -- Germans, Jews and others -- while the vast majority of the population in the surrounding countrysides were Slavs or other indigenous peoples of the region.
Just as Western Europe was -- and is -- more prosperous than Eastern Europe, so Western Europeans living in Eastern European cities in centuries past were more prosperous than the Slavs and others living in the countrysides, or even in the same cities.
One of the historic advantages of Western Europe was that it was conquered by the Romans in ancient times -- a traumatic experience in itself, but one which left Western European languages with written versions, using letters created by the Romans. Eastern European languages developed written versions centuries later.
Literate people obviously have many advantages over people who are illiterate. Even after Eastern European languages became literate, it was a long time before they had such accumulations of valuable written knowledge as Western European languages had, due to Western European languages' centuries earlier head start.
Even the educated elites of Eastern Europe were often educated in Western European languages. None of this was due to the faults of one or the merits of the other. It is just the way that history went down.
But such mundane explanations of gross disparities are seldom emotionally satisfying -- least of all to those on the short end of these disparities. With the rise over time of an indigenous intelligentsia in Eastern Europe and the growing influence of mass politics, more emotionally satisfying explanations emerged, such as oppression, exploitation and the like.
Since human beings have seldom been saints, whether in Eastern Europe or elsewhere, there were no doubt many individual flaws and shortcomings among the non-indigenous elites to complain of. But those shortcomings were not the fundamental reason for the economic disparities between Eastern Europeans and Western Europeans. More important, seeing those Western European elites in Eastern Europe as the cause of the economic disparities led many Eastern Europeans into the blind alley of ethnic identity politics, including hostility to Germans, Jews and others -- and a romanticizing of their own cultural patterns that were holding them back.