For the same reason that the Foreign Office agitated against the colour bar in the US forces stationed in Britain while defending it in the colonies.
In the early 1950s West German authorities put on exhibitions re-creating the experience of German POWs in the Soviet Union. The picture I have shows nine foot barbed wire fences and coning towers, topped with machine gun posts, with suffering Germans behind them: the very image in fact of a Nazi concentration camp (on which, presumably, they had modelled it) except transmogrified so that the Germans are the inmates and the easterners the guards.