For the past decades knowledge was "locked" behind search engines. Could you have rolled your own search engine indexing the web, to unlock that knowledge? Yes, in the same theoretical way that you can roll your own LLM.

There was never anything stopping you from finding other avenues than Search Engines to get people to find your website. You could find a url on a board at a cafe and still find a website without a search engine. More local sure, but knowledge had ways to spread in the real world when it needed to

How are LLMs equivalent? People posting their prompts on bulletin boards at cafes?

But what is (or will be) stopping you from finding avenues other than LLMs? You say other sources of knowledge will be rarer. But they will still exist, and I don't see why they will become less accessible than non-search-engine-indexed content is now.