I've talked to an Aldi employee as of late and he said Aldi is proud to now have the fastest Card processing of all the German stores (within the regulatory limits: you have to put in your PIN or sign the receipts except for those fancy/scary NFC chips) and the Cash workflow is still faster, according to their own statistics. Consider that I already look into my purse while standing in line to get an overview of my available coins and that the cashier starts to collect the likely change the moment they tell you the total amount. This speeds up the process considerable compared to the – likely more cash-inexperienced if I follow your description – American cashiers.

I can also second the opinion of many other commenters that the privacy implications of credit cards, especially the RFC ones which allow for invisible tracking, is a huge turn down of card payments in Germany.

And last but not least, as a developer, I gotta vent some air and complain that credit cards payments are huge pain in the butt, because of all those pesky special cases that arise from fraud prevention and risk reduction. Which isn't necessary for any sane payment method which can collect money directly from your bank account without the possibility of any charge-backs. This is one of the core reasons which persuaded me a European Fintech Startup Scene is necessary, so that Stripe with its CreditCard-centric API doesn't stand uncompeted.