Also, facebook doesn't just encourage soliloquys. If you're in the right groups and take care to whittle weird, creepy, rude people out, I've had some intense but wonderfully constructive conversations there.
I think the appeal of Facebook is that it seems to bring all the different platforms together. That's why even though at times I hate it and take breaks from it, I'll always come back. It combines flashy-seconds-long-"look at me!" posting, debates, blogging (you can write essentially blog posts in your notes section), interest groups, event signups, photo/video galleries, into one single interface. It's extremely interactive (in terms of the group connections and signups and "friends") , I suppose, in a way that writing on forums isn't for me.
However, take heart! I think things rise and fall in popularity again and again over time. I can say that I personally ALWAYS come back, because sometimes I need more than the intense sharing and group interaction that I get on Facebook. This is a place where it feels like I'm having a long, patient, important conversation, and trust me I may stray, but I ALWAYS come back here for that
(That and the one ultimate downfall of facebook for me is, "How the hell do I find that cool conversation again where I learned all that stuff?" The problem with Facebook is that it's all about the new, and everything in the past seems to fade away and become impossible to retrieve)