They think it's cooler with bar up?
I.m.h.o. there is nothing cool about it, just stupid.
Even though the seats are at an angle: wet seats + outerwear = slippery.
Like you said in an emergency stop a chair can rock forwards and backwards + you can easily slip of.
It's also nice to have a place to put your feet, on a long lift ride the weight on your feet can be rather annoying.
Luckily it's mandatory in Europe to ride with the bar down especially considering where the French sometimes build lifts.
Also if a young kid is alone, the lifties ask experienced people to accompany them.