schneeland
Hero
I would even extend this and say: even for me as a single person, an RPG books needs to serve different needs at different times.The books have to serve multiple purposes and audiences, with different needs and desires. Each rulebook will be a compromise of design, and you may like some of them more than others.
There is no One True Way.
When I read a rule book, setting book or adventure for the first time, I typically read it cover to cover. And to make that a pleasant - or at least decent - experience, the writing needs to be evocative enough that it creates a mental image of scenes or story fragments in my head.
But when I need the material later on when running or playing a game, it also needs to be easy enough to reference sections and parse the content in a small amount of time.
And different books make different compromises between these two things.
Now technology offers some new options here, e.g. PDF bookmarks can already be quite helpful, and VTT modules or online platforms like D&D Beyond (or it's less legal counterparts) make referencing content during play even easier. But not every game will have this and not everyone plays online, so as long as RPGs come in the form of books, the fundamental issue remains.
So as others in this thread, I do not agree that RPG books should be like manuals. At least not even they are not massively shorter - because when I look to board game instructions, which often have a much stronger focus on mechanics, even 20 pages already feel like a lot.
But at the same time, I feel the underlying sentiment that RPG texts can be much too verbose and read like badly written novels, and that this compromises the reading and playing experience, is valid. Someone else in this thread mentioned Chaosium's Runequest, and similarly I will say that my current reading experience with Call of Cthulhu makes me with presentation/layout and brevity had been much more of a concern.
I do feel, things have improved over time, though. Looking at a few things from my collection:
1. The Dolmenwood Monster Book does a pretty good job of presenting both a bit of inspiring fluff and relevant mechanics on less than half a page, leaving enough room for random tables to customize an encounter:
2. As mentioned previously, Warhammer Fantasy 4e has nice write-ups of lore spells that are both evocative and have relevant mechanics. Similar things can be said about e.g. Symbaroum or Forbidden Lands.
3. And again taking an example from OSR games: a compact presentation of adventure locations that still has key elements of the fictional world in it can be found in adventures like Halls of the Blood King.
4. Finally, to not only use OSR-related stuff: games from the PbtA lineage, such as Mythos World (screenshot from the German version) do a pretty good job of presenting both the necessary choices for character creation, but also archetype-related actions in just a few pages:
So in general examples of how to do it better than splatter pages after pages with text are already there. They are maybe just not universally applied.