I haven't seen any of these for years -- my Amazon packages always come with crumpled paper keeping things in place. Now I'm curious; does Amazon use different packaging in different locations? (I'm in BC, Canada.)
Some shipping methods you pay by the ounce, some by the pound. You'll probably see more kraft paper in methods paid by the pound, because the kraft paper is less expensive than the air pillows, and there's more slack to the next increment when paying by the pound. But for shipping methods paid by the ounce, a more expensive air pillow can keep the package from going up to the next ounce. That's one dimension of determining the proper dunnage. The other is, air pillows are more easily popped by heavier items or items with sharper edges (think blister packs), so the extra weight / shipping cost of the kraft paper averages out to be less expensive than the returns for damaged goods.
I've noticed two day airs are using a lot more air cushions in CA, US than standard shipping.
Differences in weight maybe ?
I'm betting this is it. My packages that heavy/dense enough to potentially pop air cushions if dropped seem to all use crumpled paper.
In Los Angeles a large majority of our holiday packages had one or more newer (to me) "bubble wrap" sheets instead of the Sealed Air pouches made from two 15"x15" sheets of a thicker plastic film sealed into 2" spheres (dimensions approximate).