I thought the agents are mostly self-documenting since they usually write just as much Markdown documentation autonomously as they do code/unit tests, not sure why they would need extra tools here.
You don't. But as was ever the case before AI most humans don't know to or want to have documentation written. So the tools have workarounds to try to reduce the number of "AI sucks because I told it X and it did Y" posts.
Because of old outdated info that gets left behind, causing confusion for future agents.