I'll come clean and say I've still never tried Discord and I feel like I must not be understanding the concept. It really looks like it's IRC but hosted by some commercial company and requiring their client to use and with extremely tenuous privacy guarantees. I figure I must be missing something because I can't understand why that's so popular when IRC is still there.

IRC has many many usability problems which I'm sure you're about to give a "quite trivial curlftpfs" explaination for why they're unimportant - missing messages if you're offline, inconsistent standards for user accounts/authentication, no consensus on how even basic rich text should work much less sending images, inconsistent standards for voice calls that tend to break in the presence of NAT, same thing for file transfers...

It is IRC, but with modern features and no channel splits. It also adds voice chats and video sharing. Trade off is that privacy and commercial platform. On other hand it is very much simpler to use. IRC is a mess of usability really. Discord has much better user experience for new users.

Because it's the equivalent to running a private irc server plus logging with forum features, voice comms, image hosting, authentication and bouncers for all your users. With a working client on multiple platforms (unlike IRC and jabber that never really took off on mobile).

it's very easy to make a friend server that has all you basically need: sending messages, images/files and being able to talk with voice channels.

you can also invite a music bot or host your own that will join the voice channel with a song that you requested