Facebook (and Instagram) and Snapchat have both transformed from their original incarnations, in ways that have improved the companies' valuation, but have not always improved the experience of users. It seems every single social network is trending towards feature parity with each other -- Facebook now has streaming video, Snapchat now has a decent text chat with messages that need not disappear, Instagram has an algorithmic no-longer-timeline wall and private messaging, they all have ads, even Tumblr now has IM and livestreaming. Some (important) differences remain, but from an observer time-travelling forward from 2012, the social networks of today would appear nearly interchangeable.
But there's Twitter. All these years, it has stayed remarkably close to the original concept of microblogging. Instead, it developed (or acquired) other formats and cultivated them as separate services, separate communities. It's unfortunate that not even wide societal impact can make a service profitable, or at least quell the pressure to feature-creep outside of your original scope.