IRC has advantages over XMPP by having a much wider variety of clients and the fact that you can create your own integrations for things like build automation in a very short period of time thanks to the simple text-based protocol.
I always thought it made sense in a way - it makes for a very neat separation of concerns and makes the stack more modular, since you can now use almost any combination of IRC daemon and services package.
Don't answer "bouncers" for IRC. It is an ugly hack. With XMPP the server MAY provide history, which makes it unreliable.