From a technical standpoint, too many technical writers (much less game designers writing rulebooks) lack the tools or understanding to single-source content and consistently reuse it in multiple places. A lot of rulebooks are written and designed as if repeating content is the greatest of sins, but for a game in play, _the last_ thing you want to do is make someone flip to referenced pages. You know what the text should be, just reprint it consistently where it's relevant.
But then this reveals that the problem is often inherent in a game's physical design. If a game has several discrete rules that must be frequently cross-referenced or repeated, those rules should move out of a physical book and onto cards or discrete handout items. And indeed, in my experience doing that has been the effective endgame of the "rulebooks are reference documents that lack the searchability of a reference document" complaint from this essay's writer: rather than having a comprehensive, organized, searchable reference document, find ways to move the rules into the game. Even better: find ways to move the actions allowed by the rules into the physical actions of interacting with the game, such that you don't need words to describe them.
The essay instead suggests borrowing or informing structures from textbooks and lesson plans, but the pragmatic answer isn't to make a new, better kind of game-teaching book, it's to make the rules more accessible _within the medium of the game itself_, of which the rulebook rarely or never is. The best reference guide is the one that doesn't exist because the designers recognized that it shouldn't and designed the game appropriately. The second-best is one that's integrated into the game or board as a component.[1]
In other words, and against the essay's conclusion, the necessary text to run a board game _should_ fit on the inside of the box lid: who can play, how to set it up, and how the components embody the rules. The board and components themselves should be the best, and ideally only, required documentation after that.
But that's also a fundamental design problem in games. This essay proposes a way to make a better band-aid for that self-inflicted wound, but it would be best if designers thought about how to avoid it, and that can only happen when you have know-nothing playtesters crack the box open for the first time. Alas, much of modern game design is so dense and maximalist that if you shipped a game that didn't require a dense rulebook to play, people would knee-jerk react as if the game was too simple or just awful.
1: One of my favorite recent board games is That Time You Killed Me, a time-travel-themed game with a complex conceit. It incorporates the manual as part of the game's progression, and it's flavorful, tells a story, is aesthetically pretty, and builds its rules upon itself at each step. It does few of the things advised in this essay, and if it did more of them, I think I might like the game less.
https://gamers-hq.de/media/pdf/aa/31/ef/TTYKM_Rules-min.pdf is the reference guide and core tutorial; it's 12 pages long, most of it art. The rest of the rules are in the spoiler-filled chapters not part of that PDF, each of which introduces new rules alongside a separate sealed box of new components.