Weird, I wonder if that’s the south? Up here in Lübeck, even the small stores now almost always accept everything thanks to the small SumUp terminals.
It's been a few years since I've been to Germany, but for comparison, in Norway - while it's nearly unheard of now - you also used to be able to find places that'd take "BankAxept" bank cards, which would be pretty much every domestic debit card, and is similar to EC Karten, but not Visa Electron/Mastercard Maestro debit cards.
If you had a domestic debit card, you'd almost certainly have a Visa/Maestro logo on it as well and so it'd be easy for people to assume that was what they were paying with.
But from all the comments, I’m starting to wonder if SumUp had some focus on Lübeck and Hamburg for other places to not have the huge advances in card payments of recent years.
They only took cash.
Overall it seems more common than when I first moved here, but that's starting from a low bar, I'd guess going from 1/6th to 1/2 of the cafes and restaurants.