That's because if the German government canceled the new coal plant, they would have to compensate the owners. The German government doesn't want to do that, so the plant is going forward. There's also political pressure from coal-mining regions in Germany to keep coal going.
This has less to do with electricity demand than with politics.
Also note that construction of the plant started in 2007 (ie years before Fukushima and the subsequent decommissioning of some nuclear plants). It was supposed to go online in 2011, but there were legal as well as technical problems that led to a significant delay.
This has less to do with electricity demand than with politics.