"I interpreted it as another "airbag" death."
These things happened before airbags. Plenty of people would have the car seat in the back seat all the time even before airbags. Either for safety, or because the two parents would ride in the front. The car seats are a pain to move from place to place.
Your right, but I think that air bags have made these occurences more common. When my children were young I always kept the car seat in the front. I can't envision myself forgetting a child in the front seat, but I can in the back.