XMPP did not exist on its own outside of nerd circles, while ActivityPub enjoys the support and brand recognition of Mastodon.
Jabber was widely used in the early 2000s and not just among "nerds." But Rochko would have only been 7+ years old at the time so how would he know that.
The "brand recognition of Mastodon" part makes me think this has to be a joke... right?