And instead of adding those features to existing clients, let's create a brand new protocol, server, desktop client and mobile client. Because why not?
maybe because, among many other reasons, it takes so much f time for something to change in the XMPP world, because you have to wait for the XSF to validate any change, then all the server devs to implement it, then all the client devs to implement it, then all the sysadmin to update their (very often very old version of) XMPP server, then for the users to update their clients (which, with Android fragmentation for example, is a PITA) ?