I've wondered about that. For example I've never come across any German groups at Sidmouth over the years, apart from one rather strange mob who went round chopping up logs of would while yodelling or something. No, I lie -there was a really charming and musical family group from somewhere in East Germany, just after the wall had come down, I remember them playing in the Parish Church to great effect.
I imagine it might be to do with a reaction against Nazi use of the music, or a kind of understandable feeling on the part of young Germans that they needed to turn away from a past that had gone so horribly wrong, and make a new start. And again, for different reasons, in other countries in Europe, such as England and Holland, there has been a similar turning away from their own traditions.
But there has to be all kind of really wonderful music in the background in Germany and Austria, not just the oompah stuff that gets trotted out at beer festivals and such. (I ran into one of those too on the way home from a trip to the Czech Republic. I wasn't too keen on it. But then I think Czech beer tastes much better too.)I dream of hearing groups playing tastefully folked-up Mozart the way Irish bands play Carolan.