Bluesky's website is similar to a search engine, where it just trawls everyone announcing to the world their AT stuff. It's a major goal for them to not even be able to control the aggregator.
They talk a little about it here: https://bsky.social/about/blog/11-15-2023-toward-federation
They really want to make something that's more intuitive than ActivityPub for the average joe while still maintaining the billionaire-proofing that federation gives. The tech is built from the ground up to keep them from being evil one day.