XMPP was pretty successful in the 2000s. More than Matrix so far. There were missed opportunities but the main reason it declined was Facebook and Google decided closed was more profitable than open.
Why exclude native clients?
Manager: Our users want this feature
Developer: We can't add that because it will cause incompatibility with XMPP clients
Manager: This is the 50th feature that has been blocked by XMPP and hardly any of our users use it. Time to cut off support for it
"It has come to my attention that clients which we do not control connect to our service. This severely limits the monetization opportunities available to us. Please fix before it is caught in a due diligence."