First there was friendster, which was never really that big to begin with.
Then came myspace. Achieving dominance around 2005?
Then came facebook. Achieving dominance by 2008? 2009?
Recently there have been more and more stories about teens not using facebook as much, and preferring less comprehensive sites like instagram and snapchat. more and more of facebook seems to be people posting stories about other things, with fewer of your friends sharing meaningful personal information.
I think the problem with sites like Facebook is that they begin with the notion of providing a valuable service for people THAN they try to figure out how to monetize it. People may not on a conscious level realize it, but the effort to make money off of them and the often Draconian means the company pursues such as selling your information really puts people off.
what i don't like about facebook is basically the feed becomes filled by the few people who post actively. so i miss the more rare posts by people you don't hear from often, which usually provide information of more interest. the friend who posts obama screeds or click bait articles all day, i don't need facebook for that, that's why i have twitter.