> However, teenagers have made it clear with their quick adoption of social networks such as Instagram and Snapchat they want to share everything and with as many people as possible.
Alternative explanation - teens want to share ephemerally and with a certain degree of anonymity. They don't want their parents looking over their shoulder at their friends or conversations, and seek to avoid entanglement with sections of their social network that are going to bully them or have a significantly lasting effect tied to a persistent searchable identity.
The lack of anonymity and pseudonymity on Facebook is definitely a factor. Facebook works under the assumption that we have one unified "identity" to which we can and want to tie everything we do. In reality, we share different parts of ourselves with different people at different times.
Alternative explanation - teens want to share ephemerally and with a certain degree of anonymity. They don't want their parents looking over their shoulder at their friends or conversations, and seek to avoid entanglement with sections of their social network that are going to bully them or have a significantly lasting effect tied to a persistent searchable identity.