I think what most SLF fail to realise is that air is clear, seeing turbulence is not like spotting a pothole in the road
Air crew have a job to do, they still move around the cabin because they need to, and they need to make sure that pax have heeded the sign. Exactly the same reason why crew of seagoing vessles are still moving around the deck to make sure everything is tied down in rough weather when most pax are looking green and clutching their sick bags!