There has been a gradual migration from people posting on their own websites or blogs to posting inside walled gardens or silos, like Facebook and Twitter. Sometimes the reason I hear for this is "that's where the people are." That is, there is more engagement on Facebook.
But why is that? I think Facebook's killer feature, that has made them so successful, is their notification system. Sure, people like to get Likes on what they post, but it is the notification system that gets people interacting with each other.
I remember when I first got onto Facebook. My Dylan friend from Cambridge University had sent me an email, saying I HAD to get onto Facebook, because that's where all our old friends from the long gone days (mid 90's) of the rec.music.dylan Usenet newsgroup (FAQ #1 & FAQ #2) were now congregating. He wanted my voice in the room. With some reluctance and reservations, I signed up and went to the Facebook group he had created. Almost immediately I started seeing red numbers at the top of Facebook and when I clicked on them, I was told about many people who wanted me to "friend" them, names I recognized from a decade or more earlier, other Dylan fans who I used to chat with on Usenet. It was like a class reunion, except these were people who shared an interest in Bob Dylan, people I already knew and liked. Soon we were chatting about the latest Dylan news and my reservations dropped away. It was the notification system that had gotten us communicating again.
So far we don't have something like that on 1999.io, or on the Open Web in general. Blogging on the open web can be a lonely activity. If someone reads one of our articles, they might click Like on it, but there is no notification system to tell us they did. In fact, someone might even Reply to one of our postings and we might not even notice it.
People have worked on building a notification system for the Indie Web Camp, but things get pretty geeky when you read about it. Facebook already has a system working. It seems to me that is the thing that makes Facebook easy to use and it is the reason "everyone is there."