I’m reading the ActivityPub spec here and it seems pretty fit for client-to-server communications. Yeah, it might be somewhat bulkier than your typical rest api, but it’s more universal, which begs the question: why do mastodon and lemmy both decided to implement custom (and incompatible) APIs for their clients to talk to the servers? Wouldn’t it be more straightforward if e.g. my voyager app talked ActivityPub to lemmy.world which then talked ActivityPub to lemmy.ml or something.
What am I missing?
My assumption would be that, yes Lemmy, Kbin and Mastodon use the same underlying communication protocol called ActivityPub but those have some additions which make their whole featureset incompatible to each other. So instead of writing a combined super Fediverse Browser/Explorer/whatever you get specialised Applications for Lemmy/Kbin and Mastodon.