I think it's a mix of this:
which is to say, when the Internet multiplied in size, most of the new users went to the controlled walled gardens, and content creators followed (think AOL in the early days, where ads would say "go to *URL* or AOL keyword: *WORD*". Now it's Follow Us On Twitter and Like Us On Facebook).
The "noisier" Internet you remember was the one reminiscent in Anil Dash's post, where we were all just figuring this thing out, and a greater proportion of Internet users were more proactive in their information-seeking and generating. Now giant swaths of people get their day's entertainment from Facebook and Reddit.
Also, a lot of enthusiasm for generating content just died out. There was a time when everyone had to have a blog because we were so excited to publish and be public, until we realized generating compelling content was hard, and we weren't actually
that interesting. Statuses on Facebook and Twitter have made anything but short text bursts (Blogspot, Livejournal) useless. The most successful "blogging" platform is Tumblr, and it does it by being terrible at traditional blogging.
All this to say, it's not that it's quieter, just that it's more efficient at satisfying the less-curious masses :-p