[Sohcahtoa82]

IRC would be fine if it had one feature that is expected today:

Persistence.

If you close your IRC client, you will miss anything that is sent while you're gone. You can't close it and come back to it later. That behavior is considered unacceptable today.

There's also the fact that people want and expect their communication platforms to support the posting of images and videos in-line. IRC doesn't have that.

Discord essentially is just IRC updated for the modern age.