I think this is the biggest factor. Nobody wants their family to be snooping on their every action, especially if it is a long distance family member that you n

I think this is the biggest factor. Nobody wants their family to be snooping on their every action, especially if it is a long distance family member that you normally only see a few times a year at best or someone you live with every day. With close friends you have a field of similar interests you can discuss, with total internet strangers you can say or do anything and if people don't like it then nothing happens, but with family members and parents it is a field of potential landmines for tons of kids where everything they say and post needs to be catered to not upset those who have power over their lives.