What drew me to ActivityPub in 2018 is that it seemed to be the best bet for moving towards The Decentralized Web as envisioned by Tim Berners-Lee. My interests were in particular for accessible technology that could facilitate broad participation and cocreation. The only way to make a fist to Big tech et al.
In 2017 I did an elaboration of existing technology candidates and was struck by the sheer amount of long-dead prior attempts that existed and no one remembers. The list of viable candidates was very short. Initially I gave ‘best cards’ to DAT project and started collaborating in the community, only to realize that despite excellent technical work, there was little chance of broad technology adoption. Mostly due to the deep tech focus, to the cost of attention to other success factors.
Side stepped to Secure Scuttlebutt and IPFS briefly, but they were both too immature at the time. Not likely to reach broad adoption. I then shifted focus to Solid Project and started to collaborate in the community. Only to learn about a whole range of factors that made me also scratch Solid from the shortlist.
ActivityPub had the best cards, esp. given its W3C Recommendation status, and the promise it delivered:
A network of addressable actors that exchange activities with extensible linked data payloads.
Or even..
An actor-based event-driven architecture for the exchange of social interactions between people.
With that simple conceptual architecture you can model anything.
The reality turned out a bit differently, caused by the organic growth of the ecosystem, and the social dynamics that exist in grassroots environments. Which do not really support collaboration across projects and doing work that is in the common interest to uphold the foundational technologies and standards. But that only means interesting challenges and opportunities in and of itself. 
Currently, in the time I have, I am shaping an as-yet non-existing role as Social experience designer. Consider it a Hobby. Just considering how all the tech talk relates to finding solutions that match people’s needs. And doing so in new ways that are potentially unlocked by AS/AP.