OK, I only skimmed this first time so apologies to Wolfgang for not acknowledging that I was repeating his point about the music of the imimgrant communities . .
There has been at least one sampler of German Folk Revival stuff made generally available - under a title something like "It's only Kraut - but I like it" . . I think it may have been a wider release of one of the PROFOLK CDs Suzanne referred to. Possibly worth looking out for.
One think which occurs to me - I don't know what Susanne and Wolfgang think about this - elsewhere (particularly in the UK and US) the Folk Song Revival - starting in the mid 1950s - was very much driven by the political left. Elsewhere (e.g. France and Spain) Traditional music has been an important aspect of the regions seeking to assert their particular identities (not necessarily in a divisive or separatist way). Germany's traditional music has not received either of these boosts.
On the other hand there does seem to be a strong tradition of political/satirical caberet/theatre in Germany which is hardly found elsewhere . .
As for German bands being invited to the UK - I suspect, in relation to the number of bands performing, they don't do any worse than the rest of Europe. We don't see that many European bands here, and there seem to be a lot more to choose from in France, Spain, Italy, etc . .
Thanks to Susanne, Wolfgang and others for some fascinating information.
G.