I want smaller, leaner core books.

[Reynard]

You have a curious definition of short...
SWADE is 211 6.75x10" pages counting covers.
1E was 146 letter sized pages, counting covers.

It's the skew caused by the expectation of 400, 600 or 1000 page sets of core rules.

 

[Argyle King]

I've been gaming since '79, and I've yet to find a RPG other than Sword's Path: Glory that remotely came close to that comparison.

From this thread, a disconnect seems to be between people who like to read RPG books, but play very little or not at all, as compared to people who see the books as rules for a game that is actively played (the board game comparison).

The artistic versus the practical.

I believe an rpg is both, and the books need to reflect that. It's why rpgs are a unique category of game. Individual players may lean heavier in one direction or the other, but both elements co-exist.

I would guess that I am somewhere in the middle. The reasons why I enjoy tabletop rpgs have overlap with board games, but I also have reasons why I enjoy tabletop rpgs which overlap with narrative fiction and episodic television.

To some extent, I would also suggest that having a narrative serves as an example for how to use the pieces of the game. It's a learning aide (in a way similar to why the starter sets & beginner boxes come with a pre-canned adventure). It may very well be that a particular group tosses all of that out and prefers to build their own lore and adventures. (I tend to use a lot of homebrew stuff and can understand that.) However, it is still helpful to have worked examples of how the various pieces may be used in a narrative world.

Ideally, the narrative of the book will also be used to illustrate how the mechanical parts of the rules work, using examples which aren't boring to read.

 

[pemerton]

I think game books can get away with being tightly constrained in their presentation when they're doing a new spin on a well-worn style of play (like a lot of fantasy heartbreakers); that approach doesn't work as well if they're trying to build up a whole new setting or type of play whole cloth.

Maybe. But Prince Valiant was introducing a fairly new type of play (in the late 80s), yet got away with a relatively slim book as per my outline upthread.

Classic Traveller is not quite as slim as Prince Valiant but is slim compared to (say) AD&D of its era or modern D&D. And was trying to introduce sci-fi elements, lifepath PC gen, a working skill system, etc. It is more pared-back in presentation than many games (excellent trade dress, but few illustrations). But is an amazing RPG that still holds up well 40+ years later.

So I think there are multiple factors at work that may include those but I think go beyond those you've mentioned.