For blogs in particular - this came after both geocities and livejournal. Folks had the ability to host their own websites with relative ease and to write a post history that other folks could subscribe and comment on. Blogging as a verb and Blogs as a noun really came into their own when folks decided that this sort of journal was a common enough task (and shared hosts like live journal lacked enough features) that software to easily throw together a stream of articles had common value.

That is, at least, if my knowledge of the series of events is off. Livejournal existing is about when I got into the web but that predated blogs (and particularly bloggers in the context of investigative journalism) becoming a term by quite a fair bit.