Follower bots are nice!
The toots loaded in the federated timeline are from all the followings of the instance's users. So, there are bots for some instance that follow as many possible users as possible to ensure the instance's users have an as diverse as possible federated timeline.
@PoliticalVoyeur because follow bots on twitter don't serve that purpose, they often do advertising or are empty shells to artificially boost people's follower count who pay for it.
They don't know that here on Mastodon they do server another purpose.