Asking prospective players and GMs to dig through 20 years of scattered online material (even harder to find now that posts and links in the old AEG forums are inaccessible) and find books from previouos editions of the game, on top of spending potentially as much as $500 if they want the complete 4th edition library, just to have the full system AND an in-depth understanding of the setting, is a massive barrier to entry.
This is, in part, exactly the sort of thing that motivates some of our fellow posters to advocate for a "total reboot". While a company shouldn't disregard their existing customers, it's also a terrible idea for the company ( or the existing fans ) to treat the game as an exclusive club only open to those who've either been around for two decades, or are willing to do two decades of research. As a product, each edition of the game needs to stand on its own.
Spending a page or so on the interaction of spellcasting with Rokugani etiquette, roleplaying, and the mechanics (including Glory and Honor), and adding some references in the texts of certain spells regarding their potetial social / roleplaying impact, would not suddenly make the book too massive. But as with several other requests for guidelines or a framework to build on , it's being treated as if it would be a 20+ page expansion of the book with excruciating detail about every single possible instance.
You don't have to spend 500$ and own the complete 4th edition to understand the setting... Google it, read the online story, do some research in a library, look some movies which was used as an inspirations. We live in a nice era for these kind of research, just use it...
The l5r wiki is quite good too.
The guy has done a great job keeping it up to date and resourcing all the material. And it's all free.