I didn't stop using Mumble or IRC because they couldn't, combined, meet my needs. I even prefer them to Discord on a principle basis.
But everyone I wanted to communicate with moved to Discord because it was easier -- as it had both core features which are necessary for gamers.
That's the real reason why you use Discord. Peer pressure.
Discord is in no way a replacement for a forum
I’m quite a techy person and I even wrote my own frontend to Discord a while ago, but I’ve struggled with things like bouncers and authentication to the point where it’s just easier to set up a bridge to Discord and use that when I need to use IRC, and then I miss features like editing and profile pictures (there are proposals to add these things to IRCv3 but they aren’t widely supported)
IRCCloud seems to have a good solution to some of this but is paid