Why is Poland homogeneous?

Poland was one of Europes racially diverse societys in the beginging of the 20th century. With the population being 69% Polish before WW2, with a nearly 9% size Jewish minority, however over 90% were killed in the holocaust and brutal occupation by both the Germans and Soviets. After the end of the war, only 200,000 were still alive out of 3,000,000 just six years before. However, most remaining Jews fled Poland after the war, mainly to Palestine, leaving just 60,000 by 1948. The remaining Jews left Poland during the 1960s as result to the anti-semitic laws by the Polish Government (forced by Russian Government). Leaving just 20,000 Jews remaining in Poland. Before WW2 the largest minority in Poland were Ukrainians who numbered 14% and around 4,000,000, however after the war, highly populated Ukrainians areas were annexed into the Soviet Union, as Poland's borders were pushed westwards after WW2 leaving part of aboriginally Polish lands and cities to Ukraine/Belarus. Remaining Ukrainians were either deported or assimilated into Polish society, today they number only 30,000 in Poland today. The German population of Poland after WW2 were mostly expelled. The German population during Communist Poland was 500,000, however during the late 1980s and especially during the 1990s over 75% emigrated to Germany, with Germanys right to return law for ethnic Germans. Today Germans number around 150,000, only 0.4% of the population, thus Polands largest minority. So Poland today is as homogeneous as its ever been in its history. Poles make up around 97% of the population, the largest minoritys are Germans 0.4%, Silesians 0.4%, Belarusians 0.1%, nearly all of whom are regional minoritys. Their are however recent Russian immigrants who number at around 30,000, Vietnamese 45,000, also 10,000 Afghan refugees, 4,500 Blacks, other smaller regional minoritys of Tartars, Limpos, Lithuanians, Roma, also a small Armenian population of around 4,000, and around 16,000 foreign students living temporarily in Poland to study. Non indengoius groups in Poland live 100% in either Warsaw or Krakow.