There is no evidence that they are, or that turbulence is getting worse. This is Sara Nelson and her kind at work. When a flight gets bumpy, the captain will usually ask flight attendants to sit when it gets bad. This is not that, this is declaring at the beginning of the flight that there will be no service even when the weather looks good. I've sat on smooth as glass WN and AA flights where this has happened. If I'm in Y, I'll bring a snack on board with a vitamin water, I don't care about the service on a <90 minute flight, I care that safety professionals are lying.