With Meta starting to actually implement ActivityPub, I think it would be a good idea to remind everyone of what they are most likely going to do.
An XMPP developer would likely have been delusional about the protocol he himself developed. But at the time I can assure you XMPP was completely irrelevant. AIM/ICQ/MSN/Yahoo! and maybe IRC were the tools of the day back then.
Because of actual competition (which XMPP had absolutely no part in) multi protocol messengers had their golden age then.