Without having firm data, I can see a few factors that are different. After the collapse of the GDR, it was easier for eastern Germans to move to west Germany than for Polish to move to a different country in the west. Mostly younger and educated people would have made that move, hampering future generations. With the Reunification also came the whole Treuhand issue which essentially sold off a good chunk of eastern Germany for pennies to western investors, because eastern investors had no capital. That meant the east lost out on the profits from its economy as they would accumulate in the west instead. Even today a large part of east German rentals are owned by western landlords or corporations. Then the industrial base of west Germany was setup far more for competing on the open world market with automotive companies in the NW (VW), SW (Daimler) and SE (BMW) plus the big industrial area Ruhrgebiet. So you naturally got an economic focus even after Reunification on the old BRD with the previous GDR requiring decades to hopefully catch up to the rest of the new country.