I would say they never got the stability to build a strong economic foundation. During Prussian times the port cities like Danzig and Köngisberg flourished and attracted the capital of eastern Prussia and after the WWII, they had to deal with the oppression from the soviets. The Soviets took whatever they can from the Eastern Germany and they just had to build everything from the scratch, unlike the west that got help from the other western countries like US/Marshal plan. Also when the Germany was partitioned whatever industrial base remained in the east moved to west or southern Germany because they didn’t wanted to be under socialism.

Even to this day the western German, especially the older ones considers the Eastern Germans as a second class citizens and there hasn’t been any significant investment in Eastern part to build an industrial base (except for in Berlin and its suburbs) by any government even though the west payed a tax (solidarity) especially for that.