Looking at some of my projects, it's entirely empty, or only has a few items, so I suspect it was introduced "recently" and doesn't have data from before then.
Picking https://github.com/jellyfin/jellyfin/activity?sort=ASC as a busy example, Activity page has no data prior to 7th March 2023. So it has existed for 2 of GitHub's 17 years of existence.
