Many, perhaps most, of the people who read my site have weblogs of their own. So naturally, everyone thinks they know why people blog. But it's important to reiterate, though it's rarely stated, that people have different goals for their weblogs. Being someone who's lucky enough to get to advocate weblogs to people who are new to the medium, I love seeing that "Oh, wow!" reaction that first-time weblog readers so often have.
Unfortunately, a lot of people who've had a weblog for a long time or who have been involved in the space for years think that goals for new bloggers remain the same as they were for some of us years ago. And that threatens our ability to welcome new voices and perspectives into our medium.
For example, though we have a lot of Blogdex-style link popularity or diffusion indexes, the majority of weblogs these days aren't interested in having a lot of readers. It's not that their authors are having a sour-grapes "I didn't want the traffic anyway..." reaction, they're genuinely not interested in popularity because their goals are based on communicating with the people whom they already care about, usually their friends and family.
So when I see disparaging of "unpopular" or low-flow weblogs or the use of someone's readership as a barometer of their legitimacy, credibility or importance, and I have to strongly object. Popularity is easy. What matters is that you connect.