It's also just generally easier for first-time users to start using. For anyone curious, their little "feeds" of communities you can follow in one go by topic are super handy.

For example, if I subscribe to the activismplus feed, I automatically subscribe to communities like antiwork, solarpunk, socialism, leftism, anarchism, unions, antifascism, human rights, left urbanism, etc, from a number of different instances all at once.

For a first-time user, it's easier to pick a topic they're interested in and automatically be following all the relevant communities across most instances, rather than subscribing to communities one-by-one over a very long period of time.