Yeah sorry, confused things. It's comes closer to a Mastodon thing. The point is that a big corporation like Facebook does not need to use AGPL code as long as they can just re-implement it. Compared to the total codebase used at Facebook, re-implementing something like lemmy or mastodon does not sound like a big deal. (That's not an argument against using the AGPL)

And speaking AP doesn’t necessarily make anything else compatible either, think reading Mastodon from Lemmy. The only thing guaranteed to work with no incompatibilities is other instances of the same platform. Mastodon doesn’t have quote posts, some other platforms do, they are interoperable with Mastodon but it still doesn’t get quote posts. Kbin and Lemmy used to have incompatible upvotes. This is one of the reasons Diaspora has given for not adding ActivityPub, the user experience when connecting to any other service is unpredictable.