This is an interesting article, but I don't think it's fair to blame Google for the death of XMPP. Google were the largest consumers of XMPP at one point, sure, but Google was in no way (and never has been) the market leader in communications applications. Google talk came and went, Hangouts came and went and so on. The argument of "When google pulled the plug, XMPP users had to use something else to keep in touch with friends" is equally true of Google messenger users as well. I don't know anyone that ever exclusively used a Google messenger app, now or then.

Google isn't entirely innocent here, they definitely didn't treat the protocol with the respect it deserved, but the development of XMPP was/is fraught with its own problems. I remember setting up an XMPP network for use in a small office as an internal chat tool, it was a nightmare of an experience. Different XMPP Clients had different levels of compatibility with different XMPP servers, many of the clients were just poor overall and the user-experience left a lot to be desired. All we wanted was a simple instant messenger for work, in the days before Slack and Teams. We ended up using OpenFire because it was developed in tandem with Spark, it was basic but worked well for our needs but any time I tried to adopt a different messenger, half the features didn't work.