There's also a need to be filled to let your friends know which college you're going to, how awesome your last vacation was, what job you got,... LinkedIn seems to be filling the void left by Facebook. I don't know if many people who used social media other than dedicated apps to find dates.
Facebook fails with the segregation of social groups most humans have. In some countries a person does not make true friends at work, and friends are a personal casual thing. For some cultures a friend can be made in a few days, in other cultures it takes several months or years
Perhaps that's why LinkedIn seems to be doing better: it has some selection of connections built into its premise, plus the information shared there is the minimal set that you usually wouldn't mind too much sharing across most of your social groups (got a new job, hooray!).
