A very interesting debate! As somebody who was born in the former GDR and witnessed its vanishing and transformation during the very first years of his life, I can only reiterate what many people here have said so far: Yes, it was both a combination of WW2 bombings and subsequent neglect, the latter motivated by lack of building material as well as political/ideological reasons. Old architecture (may it be secular or clerical) had the least priority since it was associated with an imperialist/capitalist past. Instead of that, building blocks were the propagated way to live in the GDR (anyway, building blocks were common in W-Germany and the UK as well). It was especially during the 80s that this decline progressed rapidly. Surprisingly, at the same time, the GDR government decided to begin the restoration of some heavily neglected places, like the Gendarmenmarkt in Berlin, but these were rather isolated cases. After reunification, the restorations were partly subsidized by the state.