IRC died for the same reason Usenet died: some old authoritative farts thumping on some ancient, bizarre rules they set during their youth, some kind of "trve" tech Islam, stopping any kind of progress and scaring away new blood.

They could enforce that kind of bizarro rules during the time IRC and Usenet were the only game in town, but everybody sane jumped off the moment remotely usable alternatives (anything web based like phpbb, shudder) appeared on the horizon.

So you cant really say that IRC and Usenet died some kind of natural death, they were simply slowly suffocated by the deranged "get off my lawn" incumbents.