It’s called XMPP, and Google ran a public gateway federating for Google Talk. Basically nobody used it, and what little use it did see was mostly third parties sending spam to Google users over the gateway, so they shut it down.
Centralized systems seem to give users what they want. This is why iMessage, FB Messenger, WhatsApp, Snapchat, and Instagram are huge, and email is dying (and XMPP failed to get any real traction in the first place).
