Ask HN: What's Wrong with IRC?

With the proliferation of chat apps like Slack, Discord, Teams, etc. why don't more companies just set up their own IRC server?

The pricing for Slack seems insane for something that was essentially a solved problem 30 years ago.

Admittedly, I haven't used IRC much and I know the UI/UX isn't the best, but that could probably be fixed pretty easily and tacked on to the existing messaging infrastructure?