As someone who runs a Mumble server (and has for over a decade) – it’s really not a replacement for the user experience that is Discord.
People want a unified UI, the ability to create communities with some amount of customization, embedded/live content, plus voice and video so they can chill and play games together. Mumble is just voice, and while it’s a very good implementation of that, it’s not even in the same user space as Discord.
Why iffy about matrix? You could always use mumble or teamspeak still
As someone who runs a Mumble server (and has for over a decade) – it’s really not a replacement for the user experience that is Discord.
People want a unified UI, the ability to create communities with some amount of customization, embedded/live content, plus voice and video so they can chill and play games together. Mumble is just voice, and while it’s a very good implementation of that, it’s not even in the same user space as Discord.