I flew regularly between Brum and Düsseldorf with Eurowings. Always had the life jacket demo. Certainly surprises me that LH don't. Maybe they reckon that with only 6 minutes over water at 30000 feet plus they are well within gliding distance to land?
Separate point: Is it not true that if flying only over land the life jacket demo is not required? Lots of lakes around in certain countries. Just saying because when you think about it the US Airways flight from La Guardia to Charlotte would have been flying over land. Yet they ended up in the Hudson!