Why the Deutschlands retained 11-inch guns

Why did Germany choose 11-inch guns for the Deutschland class?

Germany could sustain 11-inch-gun production, but did not yet have the industrial capacity for a larger weapon system.

Germany lacked the industrial capacity to build a larger gun when the Deutschland class was planned. Postwar restrictions still permitted it to maintain 11-inch-gun production for surviving pre-dreadnoughts and their replacements. This explains why that calibre remained available despite the destruction of much of the naval armaments industry. Permission to replace older ships also created an opening for further German construction.