The game is in beta, so it probably has a lot of unfinished things, and the empty biomes probably weren't designed, but they are already added to the game, so the game randomly selected them from the available maps in a given level. I haven't played it enough to determine whether such locations are repeated and how many levels are completed in this available map, but that's how I can explain it to you. Based on what I know about how the mechanics work in Diablo 2, where I spent a lot of time creating modifications for the game.