FYI: it was only during corona that a lot of restaurants started accepting card payments and before then, a typical tip in Germany was rounding up plus 1-2€ coins for a normal visit. There are still many people who aren't used to paying with card at restaurants, so the default behavior is not to leave a tip, which would be normal at a clothing store or somewhere else where people usually pay with card. Personally, I'm used to it now and the systems make it easy to leave a tip, but for a while I actually thanked the servers for asking. If you talk to them, they'll tell you that it's gotten better but in the beginning, tipping went way down when people started paying with card. You've stumbled upon an interesting cultural shift here! Now, if tipping should be a thing at all is a different discussion. 😉