There is a difference between having game assets in the disc and having the entire DLC on the disc. Game assets (textures, meshes, environments etc.) are pre-made before the game actually ships because the artists don't have enough work to do nearing the final release of the game as they are mostly done in the early phase of development and what happens next is programming, testing and bug fixes. So they start working on this DLC stuff already before the game releases and try to squeeze in as much as possible for FUTURE use on disc to reduce download times and bandwidth costs. Have you tried hosting terabytes of download through a service like akamai or your own? They are quite expensive. This does not mean it is COMPLETE content that is playable. The most difficult part, if you are a programmer you will understand, is to actually make the environment into a living world with proper path-scanning, AI, player interactable objects, event driven actions etc. This is not trivial and takes a substantial long time to do let alone get right. You think things like teleporting, oracles, time's vengeance is all automatically happens? No that takes significant code and testing and is complicated enough that even a large team of developers and testers is not sufficient to catch all the bugs (yes, I'm looking at you Atheon teleporting with the detainment shield). Yes, I know there are is that place with an "Ultra Captain" and mobs where they again put a standard placeholder enemy (a normal captain with just the name changed). This also doesn't mean it's finished content. They are standard mobs with just one name changed and behave the same way as on any area there is literally nothing special about them than being in the glitched area.