It gets stricter the further south you go, where people are more religious. In bavaria shops close earlier and can't sell alcohol after a certain time either. Overall the country is quite religious though, and especially historically has been extremely so. And something like a sunday where almost no one has to work isn't without benefits, so it won't just go away. Even shops being open on saturday past early afternoon was something that was only allowed in the early 2000s iirc.