> Deep Work, along with many other non-fiction "self help" books HN loves, could just be a couple of long blog posts.

Sure, they could be, but I would argue there is benefit to expanding them into longer books.

I haven't read this specific book, but have read several other "self-help" books and while the majority of them have shown repetitive themes, that same repetition is what ingrained the overall message the author is trying to disseminate. Reading a book over the course of weeks has a much more lasting effect on me, than probably any blog posts I've read.