Group chats are basically the Circles that Google+ saw the need for but could never get fully set up. A lot of people don’t want to share personal updates and photos to a broad swath of friends and acquaintances.
Meanwhile Instagram and Facebook keep evolving. Facebook is turning into a weird Reddit for older people. Instagram is turning into a hipper LinkedIn, where artists, musicians, and local businesses share career and business updates and advertise their wares.
Old school social networks used to be this noncommital, low-threshold way to connect with others around you. It was really great if you were a socially awkward teen or twenty-something. It's no big deal to friend somebody on facebook (or MySpace, or your universities gamified campus management system or whatever) and see what they are doing, or strike up a conversation. I really miss that kind of network.