I'd say that most of the distinction between books and blogs / other online writing is about the process and result rather than of the physical form of the product itself, though that has some bearing (see my recent comments elsewhere in this thread).
If you're familiar with the literature on writing itself --- fiction or nonfiction --- what becomes clear is how books are crafted. There's the idea, often research, organisation of notes and the like, writing itself, and then very often many, many, many rounds of editing and proofing, which go towards a result which ideally reads well, is factually accurate (where such things matter), that educational materials follow good pedagogy, is well cited and referenced, has needless fat trimmed, etc., etc.
Traditional publishing has multiple edit and filter points, from initial acquisition through revisions and translations. The upside is (potentially) well-crafted works, the downside is that many proposals don't get green-lit. The promise of the Web was breaking that editorial chokepoint, which has its own pros and cons.
Yes, of course it's possible to craft bad books, and as The Good Book notes, there is no end.
But blogging and article-writing frequently cuts many of these corners. Yes, a domain-expert can write a good blog, and yes, the process of blogging itself can be part of the process of book-creation, with feedback and corrections to the (error-prone, roughly-hewn) blog posts itself contributing to that finished product.
Books based on dialogues, lectures, commentaries, and essays are also a timeless form (Plato, Sun Tzu, Al-Kindi, Averroes, Smith's The Wealth of Nations, Feynman's Physics, all come to mind), and that's one useful way of coming up with a book-length compendium of material, though the result may lack in an overall coherence. (Overall coherence of course is not the principle goal of such compendia, rather, it is to create a usefully-curated set of realated or interacting works.)
I've been increasingly disappointed in the focus of many early digital-text pioneers on creating an end result that's specific to the domain, rather than on the process of writing works which is afforded by digital tools to increase capability and usefulness of something which, after all, ultimately is read in a linear fashion, if not necessarily how the author or publisher lineralised it. Reading is finding a path through text, the presented structure is itself only one path. We read novels through; we work through textbooks; we consult or query dictionaries, phone directories (if you remember those), and encyclopedias.
Concepts such as Niklas Luhmann's Zettlekasten, whilst analogue and paper-based are far more innovative in the sense of restructuring the authoring process itself. More modern tools would include Zotero and Calibre, perhaps.
Many books are written with less care than an investigative journalist writing their big reveal. Many books follow your process as a go-to market strategy, and not crafting a work of art.
Mike Tyson dictated his book. Self help gurus pay editors and writers to spin their 10 steps into a full "book."
Not all books use such a prestigious process. In fact, most don't.
Per my initial comment, it is not books but well crafted literature at any length. Using the term "book" to describe that is lazy and ignores the many excellent short form pieces and overwhelming amount of garbage books that get produced every day.
Investigative journalists writing a big reveal ... write with more care than most journalists and columnists.
You're cherry-picking the epitome of good journalism and comparing it as a class to all books.
The same things that go into writing a good incisive investigative journalism piece or series (many of which ... eventually emerge as books) is what makes a good book a good book. And a book offers time for that process* which a daily or weekly publication focused on current events simply doesn't have. Books trade off timeliness for quality (again, generally). Yes, there are non-topical periodicals which operate with fewer time constraints. Exceptions prove rules.
That is: there's a qualified author, assignment to a given topic, integrity in the pursuit of the story or narrative, research and editorial support in accomplishing that task, and extensive editing and rewriting to produce the most impactful, accurate, and highest-impact piece possible.
Another commonality is that those good pieces run long. A truly in-depth article probably starts at about 6,000 words (12 pages in book print, often less typeset for a newspaper or magazine), and can easily run 15, 30, 60, 90 thousand words, or more.
John Hersey's Hiroshima was published in the 31 August 1946 issue of the New Yorker. I don't find the page-count of that issue though I suspect it was on the order of 80 pages. The book version runs 166 pages, or about 80,000 words.
Hunter S. Thompson's Fear and Loathing on the Campaign Trail was serialised in Rolling Stone before being published as a book, 506 pp, or 250,000 words.
A blog and podcast I follow, The History of Philosophy by Peter Adamson is likewise being produced as a book series. The books add to what's already in the (quite well-produced) podcast.
If we instead look at most or median blogs, newspaper or magazine columns, articles (again, daily or weekly/monthly), or at the top decile of each, I think you'll find, again, that books in general exceed typical quality found elsewhere.
No need for us to continue this back and forth because I feel like I've already made and proven my point, and you yours.
The process of good literature is not unique to book writing, but it does skew long. The attempt to distill knowledge or storytelling into its shortest form does have severe limitations.
Writing that is short in length is more likely to lack value, and vice verse. As a rule.
However I still must insist my original point, that saying you are reading a "book," while on average means what you are reading is more valuable than say a tweet, is not NECESSARILY indicative that you are reading something GOOD. The term "book" is not a synonym for "good literature."
It is possible, however unlikely, that reading a great piece of relatively short journalism can be infinitely more valuable than reading a book written by a complete idiot.
But of course I will cede that books are usually better, and long form content is usually better.
Although I have to say the dream of many writers is to be as succinct as possible, which means shortening language. The idea here is that good writing would become shorter and shorter over time.
If you're familiar with the literature on writing itself --- fiction or nonfiction --- what becomes clear is how books are crafted. There's the idea, often research, organisation of notes and the like, writing itself, and then very often many, many, many rounds of editing and proofing, which go towards a result which ideally reads well, is factually accurate (where such things matter), that educational materials follow good pedagogy, is well cited and referenced, has needless fat trimmed, etc., etc.
Traditional publishing has multiple edit and filter points, from initial acquisition through revisions and translations. The upside is (potentially) well-crafted works, the downside is that many proposals don't get green-lit. The promise of the Web was breaking that editorial chokepoint, which has its own pros and cons.
Yes, of course it's possible to craft bad books, and as The Good Book notes, there is no end.
But blogging and article-writing frequently cuts many of these corners. Yes, a domain-expert can write a good blog, and yes, the process of blogging itself can be part of the process of book-creation, with feedback and corrections to the (error-prone, roughly-hewn) blog posts itself contributing to that finished product.
Books based on dialogues, lectures, commentaries, and essays are also a timeless form (Plato, Sun Tzu, Al-Kindi, Averroes, Smith's The Wealth of Nations, Feynman's Physics, all come to mind), and that's one useful way of coming up with a book-length compendium of material, though the result may lack in an overall coherence. (Overall coherence of course is not the principle goal of such compendia, rather, it is to create a usefully-curated set of realated or interacting works.)
I've been increasingly disappointed in the focus of many early digital-text pioneers on creating an end result that's specific to the domain, rather than on the process of writing works which is afforded by digital tools to increase capability and usefulness of something which, after all, ultimately is read in a linear fashion, if not necessarily how the author or publisher lineralised it. Reading is finding a path through text, the presented structure is itself only one path. We read novels through; we work through textbooks; we consult or query dictionaries, phone directories (if you remember those), and encyclopedias.
Concepts such as Niklas Luhmann's Zettlekasten, whilst analogue and paper-based are far more innovative in the sense of restructuring the authoring process itself. More modern tools would include Zotero and Calibre, perhaps.
<https://zettelkasten.de/introduction/>