Why not? Each room in that context is its own "product."
-O
Because that's what the license says.
Could you create individual rooms in standard html / blogging software? No. (not a format supported by Section 3 and specifically called out in 5.5)
Could you create individual rooms and publish each in a separate pdf? Yes.
Can you link those rooms together with an overview map and have the users come back and download them as necessary? No. (Stops being a single-download book format as you need multiple downloads to acquire the dungeon.)
Can you create a variety of pdfs that represent the adventure as it grows day by day so people can download their preferred point in the product evolution? Yes. (Each pdf is self-contained and would count as a single-download book format)
Do these rules make a whole lot of sense in this situation? No.
GSL Section 3 said:3. Licensed Products. The license granted in Section 4 is for use solely in connection with Licensee’s publication, distribution, and sale of roleplaying games and roleplaying game supplements that contain the Licensed Materials and are published in a hardcover or soft-cover printed book format or in a single-download electronic book format (such as .pdf) , and accessory products to the foregoing roleplaying games and roleplaying
GSL Section 5.5 said:5.5 Licensed Products. This License applies solely to Licensed Products as defined in Section 3 and to the specified uses set forth in Section 4. For the avoidance of doubt, and by way of example only, no Licensed Product will (a) include web sites, interactive products, miniatures, or character creators; (b) describe a process for creating a character or applying the effects of experience to a character; (c) use the terms “Core Rules” or “Core Rulebook” or variations thereof on its cover or title, in self-reference or in advertising or marketing thereof; (d) refer to any artwork, imagery or other depiction contained in a Core Rulebook; (e) reprint any material contained in a Core Rulebook except as explicitly provided in Section 4; or (f) be incorporated into another product that is itself not a Licensed Product (such as, by way of example only, a magazine or book compilation).
* Highlighting has been added.