I've never got it either. I do have to say though that the German society is super focussed on cash as a thing so I wouldn't be surprised if the associated cost of it were lower there.

It doesn't make sense to me however that the economics are ostensibly so different between e.g. Germany and France, where in the latter basically even small shops don't care. Either it's something to do with taxes like you said, or German shop's margins are razor thin.