As much as some of us love having something to collect, it's probably not enough to justify the production costs of a physical version. Especially when you don't actually need anything to play the expansion except for the 20-some digit code. The game will have to be updated online at first and subsequent runs, so any software on the disc will be obsolete before it even gets installed, and we don't package games with comprehensive instruction manuals anymore, with all the info online. For people who really want something to collect, they make CEs that are all about the fancy extras that we can put on our shelves.