I thought the whole point of ActivityPub+Git was to replicate the social aspects of GitHub. I think developers don't really have experience working with email either, so they go with what they know best (web).
Honestly if you compare the two, email is much easier to grasp. So I'm not sure what the point is. If you want easier, then go with email.
That said, I don't understand why a decentralized system shouldn't speak as many languages as possible. Therefore I see no harm in implementing both.