And a lot of people who use it have never used IRC.
And it has an app that has the same name as the service. That makes it a whole thing, like Instagram or TikTok. It's really eye opening to see the number of people who never considered that reddit the app is a separate thing to reddit the service/site.
The wider IT community is still very much a small niche. We often forget that.
I wouldn't agree. Aside from Slack, Discord built the next highest quality browser-based chat and voice app, targeting consumers vs enterprise. It's well engineered, reliable, and has a simple user interface (mostly).
Video & voice on slack is pretty bad.
I've always thought their video conferencing was better than Google, but eventually zoom just took over. Never tried voice and felt like that was just tacked on because it became trendy due to Clubhouse etc.
That would be enough by itself.
But it's so much better than IRC in so many ways. Sure, you can run your own IRC bouncer for Libera on that "shell account" or AWS micro-instance you're always running anyway, but who except the nerdiest wants to do that? Even then, you don't get to see past messages when you join another channel, unless there's some history bot or archive page, both of which are clunky. Also don't forget to do the NickServ rituals with each network. And you still don't get good multimedia, which most users expect now as normal communication culture.
Throw in a good UI (compared with alternatives except maybe Zulip, and not including search!), link previews where the sender knows exactly what the receiver will see, markdown-style message formatting, enough metadata to link replies, and succinct emoji reactions that don't spam the channel, and if you feel like using them audio and video conferencing that just works with no additional setup.
I say all that as someone who used to use IRC daily, including running an archiving bouncer and admining a community channel, but I no longer bother. Admittedly because I was busy and ill for a while I lost my registered NickServ username (it expired), which also ended up breaking channel admin, so that was a bit demotivating. When everyone left Freenode for Libera, I just stopped using IRC.
I also say it as someone who strongly agrees with the Discord complaints about projects using it in such a way that most of their useful documentation is being continuously created then effectively lost now.
To Discord's credit, they made a great quality, polished product with an understandable network effect. But it's a shame it's not easy for projects to make their channels publically archived and searchable, and of course it's a shame it's neither an open network nor an open source product. And that the search and search UI are awful.
I'd say given the types of projects I see using Discord (mostly open source, even the commercial ones), Matrix still has a chance of taking over eventually, if Discord doesn't open their network somehow. But there's a high friction against it, both for existing projects because their chat history and users can't be transferred, and for new projects because of their need to meet users "where they already area", i.e. on networks (Discord, Slack, Telegram etc) where the users you want tend to already have accounts and apps already running.