literally the story of google itself... built technology on a large corpus of existing text (the internet) for pagerank and then able to leverage and monetize it via search and ads.
When a model trains over Reddit, it may still provide a service that is free. But the way it's going, companies are charging money for access to those models and aren't generating traffic for the underlying training data/sites.
But make no mistake, the secret sauce in Google Search is by no means open, and possibly not even comprehensible to a single human at this point.