Shouldn't they be called "Anti-Trauma Backpacks"?
As I've mentioned somewhere else around here, in my suburban jail (pop. 2,500) setting we have four rolling kits, each weighing almost twenty pounds, with nursing level stuff, and each designated to meet up with one of twenty BLS and first aid-level twenty pound duffelbags on a scene. I myself have heavily affected the contents of these, mostly by trimming and eliminating after the busybodies load them up with Tinactin, bagbalm and Telfa pads; however, in the vast majority of instances I handle the calls with my eight-pound, mostly first-aid level ( a little nursing and BLS stuff not much) kit in a padded nylon camera bag, and 1/3 the cubic space in that is used up by a SAM splint I've used twice in six years. Short distances (up to 1/4 mile), rapid outside competent EMS response, equals don't need backpack. The big kits are a welcome measure of preparedness and are occasionally used, but a shoulder suspended kit would be less effective and efficient.
PS: the only point higher than a second story is the tower; I'd want a backpack for stairs. Or a probie!