Aye great read and very illuminating. We gotta protect the fediverse from corporate insidious destruction. This quote stood out to me:

And because there were far more Google talk users than "true XMPP" users, there was little room for "not caring about Google talk users". Newcomers discovering XMPP and not being Google talk users themselves had very frustrating experience because most of their contact were Google Talk users. They thought they could communicate easily with them but it was basically a degraded version of what they had while using Google talk itself. A typical XMPP roster was mainly composed of Google Talk users with a few geeks.

In 2013, Google realised that most XMPP interactions were between Google Talk users anyway. They didn’t care about respecting a protocol they were not 100% in control. So they pulled the plug and announced they would not be federated anymore. And started a long quest to create a messenger, starting with Hangout (which was followed by Allo, Duo. I lost count after that).