There's really not. A bunch of people thought the same thing about Middle-Earth, and how very much Tolkien scribbled about it, with fill-ins in the appendices. And Iron Crown wound up writing thousands of pages of setting material in consequence. (Being one of those writers, I'll be happy to expound on that until your ears bleed.)
But sure, let's take on your presumption, and make the rather amusing assumption on top of it that you can keep a gaming group satisfied with NOTHING beyond the walls of Hogwarts for anything beyond a strictly railroaded one-off. The players are likely going to want:
* A complete list of what courses are taught;
* A complete map of the grounds;
* A complete list of professors;
* A good many more NPCs named and statted out;
* The magic system defined, in detail;
* A notion as to how many students are actually enrolled ...
How long are class periods? What kinds of magical herbs/potions/materials are there, in what quantities, and what do they do? What are the layouts of each House? What are the exact stats of Veritaserum -- duration, resistability, color, scent? How many unused classrooms are there? (And come to that, doesn't that suggest that Hogwarts used to have a lot more students, and therefore in consequence, a fair bit of empty dorm space?)
And good grief, how much precisely is in the Room of Lost Things?
Rowling didn't set out to write any of this. And in sober truth, she wasn't out in the first place to write a world that could resist deconstruction from hundreds of thousands of fanon-hungry fanfic writers or gamers. She was out to write an entertaining series of children's books.
IDK, man. WEG Star Wars was one of the most well regarded RPGs ever—not just licensed, but RPGs in general—and it didn't include half the level of setting details you seem to be expecting here. Most of it was stats for different types of creatures, weapons, vehicles, etc. But when it came to describing actual planets and such, it just included a handful of them, with just a couple of paragraphs each as "sample" planets and most of the info was guidelines on how to come up with your own planets. The bulk of the game was game rules, and they didn't even include details on what kind of materials you need to construct your own lightsaber.
So is there a possibility that some people would bitch that you didn't include the recipe for how to brew Veritaserum? Sure. Gamers are a whiny lot. But how many games include that level of detail anyways?
Some of the stuff you mentioned here seemed pretty doable, though. The biggest obstacle would be getting the OK from Rowling, which I didn't even dispute was an issue in my post. But you could add a bunch of teachers from the books, plus maybe make up a couple of new ones, along with guidelines for how to come up with more teachers, given that they tend to change a lot and some of them die.
A map of the grounds seems doable, given that people have done similar stuff for other games. And there's been HP video games, so people could use those as a starting point to get a general idea of the layout. Again, getting the OK from Rowling might be an issue, but in terms of actually drawing up a map it could be done. Same for the school interior, though, that would obviously be a lot of work. But people have done mega dungeons, so a map of Hogwarts shouldn't be an unsurmountable task. But you could also include guidelines for GMs coming up with their own secret rooms and such, given that characters in the books would sometimes find hidden areas, so there's precedent for unknown sections in the books.