CapnZapp
Legend
No, I meant that the reason isn't "that individual DMs can create their own stuff". That's bollocks. That would assume DMs are unable to expand on existing maps if these don't indicate large unexplored areas, as if we somehow need explicit permission to expand maps, which is obvious nonsense.The real reason is that they had 320 pages, not 3,200 and wanted to get to the lower levels.
Instead the real reason is that WotC nowadays never does more than they think they can get away with. The ethos of going the extra mile is lost.
PS. Unlike other posters I don't want or need 320 pages of semi-random dungeons, let alone 3200 pages. You might have confused me with someone saying "this product is bad because it details a huge dungeon, not a megahuge dungeon". To me, that sounds like sheer insanity.