I think you are mistaking source for distribution channel. The "internet" doesn't produce anything it just distributes it very cheaply.
I can go to a local library and view newspaper articles on microfilm.
But where can I go to find forum discussions and cat videos that were produced before the internet?
Nowhere, because they didn't exist. The internet (and applications built on top of it) encourage and facilitate creation. It's not just about distributing content that would have been created anyway.