The simple answer is because I don't know how to do a semantic search on a bunch of documents, nor do "plain old vector distances." It's not my field.

The longer answer is that I think that it will also be useful to have the background knowledge (however hallucinogenic) that ChatGPT has. I'd like to be able to have a conversation specifically grounded in the papers, and if I ask about a topic that isn't specifically mentioned by those words in the article, I'd like it to be able to say "none of the articles talk about X, but they do mention Y, which is related in this way." I'm not sure if this is expecting too much of it.