The writing was on the wall before that, though. WhatsApp was eating everyone's lunch and Facebook / Google wanted to move faster and own the messaging space.

Afaik facebook was designed to be a closed walled garden from the get go and never offered interoperability despite using xmpp at first.

Google gtalk predates facebook and happened at different times, IIRC the change to a closed chat service was a reaction due to facebook abusing the openness to scrape contacts.