>many communities have moved from the open internet into Discord

This was a feature.

This was desired.

This was welcomed by all actors involved.

(You're not an actor but a spectator, unless you own a Discord server)

I "own" a Discord server for my WoW guild and I'm not particularly happy about being on it, but it's the default choice for gamers and voice chat. It would kill our raid team's recruiting if we told people they had to install some obscure service instead of Discord if they wanted to raid with us.

These are just network effects.