My husband used to play tennis with an Adolf who was known as Dolfie. He was as unfortunate as his name. But, remember that Winston has gone just as much out of use as Adolf. Does Louis get much use in France? In other words, is it a matter of name fashions being cyclical, or are some associations just too strong?
And I had an honorary auntie Frieda, a German woman, who lost her German accent completely when she hit South Africa and very mysteriously called herself George - and so did her husband, Bob. Go figure.