From my perspective as a dev, the question I find myself always asking is "Who's the SME that can I ask about this code that still works here?" So for me the benefit of your project would be using it basically as an intelligent git blame that says who's done what to a particular line/file/module/project, and why. If that SME isn't available anymore, I'd like your tool to help me build context around the issue I'm working on. I'd want to see at least git commit message history and authors included in the available knowledge. If the repo has docs included, even better.

Another reason I would want git history included is because I think it would make your product more valuable quicker. I see your tool as a way to improve the dev culture by promoting the points you mentioned, but it's not clear how long it takes it to start to pay off and be able to answer some of the more historical questions you've suggested. I question, if my team had poor/nonexistent PRs in the past, when would I be able to get any use out of it, and would there always be blindspots around code that didn't have a good PR.