In my personal experience the 'requirement' of some companies that data must be hosted in Germany is their own internal policy rather than something that is prescribed by their reading of the law. However there have been some court rulings where servers hosted in Germany are applied additional restrictions over servers hosted in Ireland.
A lot of this may also have to do with own interests. In the 80s and 90s every EU country wanted US silicon fabs in their underdeveloped regions. Now every country wants hosting farms.