I think board games on the more complex end are running into the fact that they're goddamn near impossible to teach, or to learn well enough to teach, without watching a demonstration or playing a couple demo rounds. A book alone is simply not sufficient without, as the linked PDF complains about, something like the effort of studying a textbook, probably with the game-pieces right alongside and working through fake play as you go so that any of it makes sense.

Attempts to translate that into extensive game walkthroughs in manuals (not quick examples of play to demonstrate a rule, which are sometimes nice) are horribly misguided. Just include a damn QR code that points to a YouTube video. Give it an entire page to make it more likely the players find it, that'll still be less space than a walkthrough.

I truly think Monopoly's around the upper end of complexity that normal people can be expected to absorb and apply from a game manual—not from someone showing them the right way, or from a video—which means the vast majority of modern-era games are way past that point. I've known more people who fail to play with all parts of the Monopoly rules than I've known people who correctly play with all of them (or at least know the rules, but affirmatively reject or deliberately modify them) by a large margin. Usually it's auctioning or mortgaging they skip, either because they never read the rules and learned from someone who wasn't familiar with those parts, or because they did read the rules but deemed one or both of those parts too daunting to play and manage without having seen a demonstration of it and decided the game seems like it can run without those rules (yes, it can, but it makes it worse in some key ways—not doing auctions when someone declines to purchase a space is especially harmful, as it prolongs the game without much in the way of compensatory extra fun)

Like, sure, Risk is kinda a shitty grand strategy or area control or war game or however you want to classify it, for demonstrable, if arguable, reasons, but if your answer to that results in more complex rules than Risk... you're gonna need an explainer video, because your rule book is definitely gonna suck. Because that's a game normal people can, just barely, often figure out and run correctly just from the rule book, and yours surely won't be.