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.
Basically keep people from using all the other platforms. Then stop supporting them. Similar like .docx never quite works in the open document editors. At least i refuse to believe that OSS devs are less skilled and motivated.