Discord’s video quality is pretty mediocre. If you’ve already got a home server somewhere and a decent internet connection, streaming 1080p or higher over this probably works better than streaming over Discord.
You can buy Discord premium or whatever it’s called, but that’s priced high enough that a home server electricity bill or even a VPS with pretty decent specs can be had for the same price.
As for why you’d go through the effort: same reason Linux users don’t run Windows, because they like the philosophy or because they want the control over their stuff.
Edit: also, streaming games from Linux through Discord still doesn’t support sound. I work around this by using Pipewire’s ability to re-route game output into the microphone input stream for voice chat, but that’s just a stupid workaround for Discord’s bad service.