Facebook never federated so their implementation was just an API they couldn't control to them:

> Facebook Messages are evolving to allow people to share rich content beyond text: photos, videos, audio and even stickers. We want to ensure the best possible send and receive experience where all these rich forms of content are reliably and consistently available on every platform. XMPP doesn't support all these (and future) content types, and it's difficult to ensure an XMPP client is rendering them appropriately. As such we've decided to sunset the XMPP Chat API.