I wish I knew exactly how popular Newgrounds is. There was this comment on a Youtube video that was only five days old saying that no one had mentioned Newgrounds there for years. Random, I know. But exactly how large of a niche does Newgrounds occupy? It's not mainstream, right? How does content proliferate from here to those other sites developers don't own and all... I don't quite understand the way the internet works I guess LOL.
AliceMako
Content proliferates the same way everywhere, people link things then they end up in different places for starters.
Things get reuploaded, licenced out, sold off, stolen or handed to spreaders and statwhores to farm traffic. Something really typical is for people to post their content in multiple places to begin with in hopes of maximising their revenue stream.
Newgrounds is like the original proof of concept everyone their grandma and their dog included copied, it's never really been mainstream even at the peak of it's popularity though any rube can tell you we wouldn't have a mainstream as we know it today if it weren't for newgrounds.