Extra shock absorption in the packing material that allows you to ship the rack with equipment installed.
I ordered a bunch of specialty racks (4 sets of 12-24 tapped 23" rails in a 44" deep cabinet, for example) for 3 different sites a few years ago, via Graybar from a manufacturer not mentioned here. Each order (delivered by different carriers at different times) had various damage which required either replacement parts (doors, side panels, missing rail hardware) or whole replacement cabinets. One of the cabinets was actually bent into a parallelogram shape on all 3 axes. I figured this was shipping damage (despite the multiple carriers involved) until I discovered that one of the cabinets had been bashed before being painted and was packed inside an undamaged multi-layer cardboard wrapper and then shrink wrapped.
This has led to an ongoing joke that "the factory is very concerned about shipping damage, so they smash them at the factory before they ship them to make sure".
I'm sure my Graybar rep will cringe when I ask for a quote for another rack in a few weeks...