By now, most users have peeked at Instagram’s new private messaging system. From an outside perspective, it may seem like this isn’t ideal because it’s not as easy to share as say, a public Instagram picture. Mashable explains why social networks absolutely love private messaging here.
In short, people want social platforms that can mimic their real life. They want private groups, they want to broadcast to a smaller audience of just a few people. Also, if Instagram accesses this data- what everyone is talking about in private- they can more easily sell information and track what people will be taking about tomorrow, in public.