Blog posts give you 4 hours to write, backed by years of life experience, probably based on things you've had on your mind for a while.
Magazine articles pay you to write what the audience/advertisers want to see. They've got to be a net negative, convincing someone to write when they didn't necessarily want to, to say something they didn't necessarily want to say.
Books are an item for a CV or resume, and a status symbol. Sure there are respected textbooks, but there are a lot of worse books out there than respected textbooks. Look at "Why we sleep" recently - years to write, torn apart by one blog post. Look at bestseller lists rigged by false purchases. Look at tech books where writing a book on a language or tech stack is almost more of a status grab, or at worst a "teach myself $thing by writing a book about it" than a long standing tome.
(Also, 8 hours to read a book??)