I think Eldar Kersebaum is the closest with the answer; Germans just are used to it. And eventhough Germans and Germany is always thought to be very tech-savvy, but when it comes to new technologies they are one of the most sceptical and old fashioned people you are going to find. Yes, in Germany money behind a plastic card is still considered as a "new technology".

You would be surprised how few places actually accept Debit cards (ie. EC card), not to even mention Credit cards, in Germany. As a Finn living in Germany, this has been probably the single biggest "cultureshock" between these two countries.