I've been riding chairlifts for 46 years and didn't give much thought to the bar issue until recently. As people get older, sometimes they get dizzy in flat light. I watched my 80-year old father repeatedly fall during a snow squall in flat light. He couldn't get his bearings, got dizzy, and just kept falling over. That can happen on a chairlift as well. For older people it's sometimes an absolute requirement to have a bar on the chair, and that it be down.
At my local mountain Heavenly the bar is usually up for people from California or other western states, and down for everyone else. The chairs are all pretty close to the ground there, but over at Kirkwood chair 10 used to scare me in high winds before Vail installed bars on every chair. Another notorious one is Chair 23 at Mammoth. It has no bar, is really high off the ground with a long span, there are no trees, and it can be super windy. It's a white-knuckle ride even for me with 10's of thousands of chair rides over 46-years.