For the same reason you might make a movie instead of shooting still pictures. A blog is a collection of isolated points. Readers can connect the dots, but the medium doesn't lend itself to comprehensiveness or to narrative threads. People read a book all the way through in a day or a few days. People read blogs in dribs and drabs as they have time. They miss things, they're distracted, they go on vacation. If you want to paint a big and coherent picture, a book is still better.Well, I tend to read books in dribs and drabs, and then often set them aside and never go back. A blog is a continuing relationship with a writer, so it actually could end up feeling more complete and coherent than an author's book. But in any case, books are different from blogs, and the form the writing takes is part of what affects the reader's mind. Both are good in their own way.
I was struck by the effect of Richard's book "Only What Is," which arrived in the mail the other day. Richard -- my ex-husband, Richard Lawrence Cohen -- simply had a book manufactured out of 89 blog posts. I still can't get over how differently I saw the writing that I had already read on his blog. Why was that? Was it specific to Richard's writing? He does blog posts that aren't so much about exactly what's happening now, and perhaps he always saw his blogging as the composition of short short stories that he meant to have in a book and was just storing temporarily in his blogspace. A blog can be a notebook for someone who is always really writing a book. The solidity of the very same words when bound into a book amazed me. It gives new meaning to the word impressed.
I'd have a hard time doing what Richard did, collecting favorite posts into something that would work as a book, because the posts are set in a time frame and caught in their links. What, would you turn the links into footnotes? Or would you have to select not your favorite posts but the posts that were the least timely and dependent on links, that is, your least bloggy posts? It might be an interesting exercise to discover what those were.
What Glenn did is different. He derived ideas from his experience with blogging (and other things that are like blogging) and wrote the book as a separate project. Obviously, his blog also works as a way to promote the book now, and it has over time won a large set of readers who will tend to feel motivated to buy the book.
Will the Althouse blog ever produce a book? Who knows? I started a project a while back, but I outgrew it. Things are always tumbling along into the future on a blog. Everything that's a day old seems so over. Writing on a blog is like living in the present. It feels so right.