Think about when the term was invented. It wasn't in the days of IRC, ICQ and forums. It wasn't even the launch of facebook (2004). It only came up after people used their real identities and got algorithmically addicted to spend more of their time on a given platform.
If you want to retroactively attribute the term to things, you'd also have to add it to newspapers featuring reader's letters. But that's not what social media is.
If you want to retroactively attribute the term to things, you'd also have to add it to newspapers featuring reader's letters. But that's not what social media is.