Discord is a centralised IM + basic forum with commercial polish.
Small communities can't afford site hosting and moderation, FOSS alternatives like Matrix are significantly inferior products. Fandom killed independent wikis, Reddit killed independent forums.
If Discord ever goes down, there will be decentralised services competing and advocating freedom until a new centralised service takes all the users for itself, just like Mastodon and Bluesky.
That was all nice for a few years, but it was clear it can't got like this for ever - and here we are.
This is exactly the reason cited for several non-gaming discords I'm in.
I guess thats changing though, I see Youtubers all over the place now watching these things like a hawk. Referring to the Highguard scandal.
Discord IMO won because of a killer trio: 1) good comms 2) full history 3) faster UI over bloated Slack.
It won by simply building a vastly superior product during its growth phase.
For gamers, it replaced fragmented, clunky, or paid alternatives (TeamSpeak, Ventrilo, Mumble, Skype) with a frictionless, free app that had excellent voice quality and modern UX.
It worked so perfectly for gaming communities that non-gamers inevitably took notice, realizing it was effectively a better, free version of Slack for community building.
But that was the user-acquisition era. Now, we're seeing the classic enshittification phase.
Every other notification badge is an alert trying to sell you something. I still use it, but the product development focus seems to have entirely shifted to selling $9.99/month "blinky bullshit." I understand they have to monetize eventually, but it's exhausting.
Ultimately, it got big because for a few years, it was undeniably the best, cleanest chat client on the market. It was just relentlessly good for the user.
Whether it stays good, or follows down the Microsoft path of turning into a full-on ad-distribution network remains to be seen. But right now, despite all the crap sales, it's still pretty good... (=