I agree! I think there's a level of didactic intentionality that the effort of publishing a book mandates. A blogpost or Stack Overflow answer or wiki page is typically more like a reference for a particular topic; finding 300 contiguous, organized pages that cover the breadth and depth of a topic on the Internet is not common. The only thing that comes close in my experience is a subset of online courses, the ones that seek to give a foundational understanding more than a step-by-step tutorial of how to make something happen.