The other big reason for that design is storage density: it trades off fast random access for storage density (since things are all stacked up on top of each ot

The other big reason for that design is storage density: it trades off fast random access for storage density (since things are all stacked up on top of each other). This makes a lot of sense for last-mile deliveries around densely populated (and thus expensive real-estate) areas. (Though as pointed out, autostore had a very similar concept for a while before).