It did happen, though. Just not in the same way. When it gets to the point where notifications are too spammy, it's very
very easy to direct things to use a different channel and it works at huge scale. Anyone who uses IRC more than casually via some web portal is capable of being in more than one channel at a time. Google SRE still uses IRC internally specifically because it always just works and does what people need it to do.
One of the downfalls of IRC is the notion that everything should happen in the chat. There's no reason you can't have a pastebin and a file server and screenshot sharing service, most of which don't matter anymore after 5 minutes anyway. It works really well and in fact, we kept using them after switching to fat chat because it was a better experience. There are reasons to want a fat chat client (primarily mobile, imo), but having used both for many years, the featureful chat client ends up being worse than just sharing links most of the time.