Earlier quoted context omitted.
People don't want to join "an instance". People don't want to care about what "an instance" is which also means being asked to be aware of things like instance-specific moderation rules. And I don't know what it's like now, but cross-server following used to be quite annoying.
People join "rooms", "lobbies", "boards", "subs", "groups", "servers" and the like all the time, and deal with moderation rules.
There are major differences between "subs"/"rooms" that are fundamentally joined and independently operated protocol hosts that are fundamentally not.