Excepting the occasional time that a certain piece comes to matter to people for some reason or another, a blog exists in an eternal present. It is about the now. That it's usually a single author, often about a single topic, makes it like a degenerate form of newspaper.
And unless there's a reason a piece garnered particular interest, a blogpost from a year ago is a like a newspaper from a year ago: a valueless artifact.
Why would I spend my time writing something like that?