Those meat packages end up getting very different handling, because of the dry ice that's used to keep them cold. It's necessary to keep a careful track of the dry ice and know how much of it you're loading into a container, in order to avoid asphyxiating your colleagues. Most packages are just tossed along as quickly as possible, because there's a tight schedule to keep. But you have to temporarily slow way down when a package containing dry ice comes down the belt.

It's a little bit like that photographer's trick of packing a starter pistol with your camera equipment when flying, in order to ensure that the baggage crew is extra careful with your stuff.

Source: I used to schlep packages at a UPS hub.