I guess were were in Austria when these backpack/lift incidents happened.
I always carry a day pack. It's small, can easily ride up over the back of most lifts and isn't that deep if it can't. Why? I have terrible temperature regulation. Thus I have goggles, an extra set of gloves and an extra mid-layer if I guess wrong on weather. Or I can dump/switch out what I'm wearing if it's too warm. And usually a water bottle. So don't tell me I can put this stuff in a jacket.
Lapping lifts, I think it's a nuisance to undo and redo backpack buckles. Most places with a backpack policy I just undo the chest buckle and swivel it around on my lap. If I have to undo the waist buckle too, that's a much bigger PITA, and having those waist buckles dangling is much more likely to get one caught on the lift.
Here's the weird part. You would think it would be the big corporate ski areas that would have a nanny state rule like this. But no, it's the mom-and-pops in Canada where I see this: Red Mt., Castle Mt. and Mt. Baldy on this year's road trip. And DanoT says Sun Peaks too. The Stairway to Heaven lift at Kicking Horse has always had a backpack carry policy, but half my rides there I'm in the gondola anyway.
Meanwhile as yet I have never seen a backpack policy mentioned at Mammoth, Alta, Snowbird, Whistler or any MCP or Vail Resort. I sincerely hope this obnoxious rule doesn't spread.