Facebook is (generally speaking) for people in their mid 20s and up who have become adults. Instagram is for artsy people who share photos, but is primarily used by teens - early 20s.
But Facebook is a good enough platform, so why? Teens will always seek out places where they can be their usual obnoxious selves without the prying eyes of judgmental adults. Instagram isn't the destination for teens, it's just a waypoint until the Instagram users grow up, and then there'll be a new network that everyone will flock to.
In the end, Facebook will still win. Ignoring the fact that Facebook owns instagram, the Instagram users will get married and have kids, and they'll want to share those moments with their parents and grandparents on Facebook. It's still the most widely used AND most robust of the social networks.
But Facebook is a good enough platform, so why? Teens will always seek out places where they can be their usual obnoxious selves without the prying eyes of judgmental adults. Instagram isn't the destination for teens, it's just a waypoint until the Instagram users grow up, and then there'll be a new network that everyone will flock to.
In the end, Facebook will still win. Ignoring the fact that Facebook owns instagram, the Instagram users will get married and have kids, and they'll want to share those moments with their parents and grandparents on Facebook. It's still the most widely used AND most robust of the social networks.