A bit of humour and honesty usually works and dampens the agitation. Pax expect and respect being treated as intelligent adults and not school children who will do as they are told, because you tell them to.
Lowly ground staff are often not employees of the airline and so have little loyalty. They are not the most motivated link in the chain. "Operational reasons" is too bland. The airlines will try to get away with not having to carry the blame and thus compensation. It will always be smoke & mirrors unless it is obvious. More than once I've been a pax and listened in to ground staff conversations at the gate and discerned there was a crewing problem and not an ATC delay; but guess which we were told?