A town hall is not a party
An all-hands or a members' meeting lives or dies on a different thing than a social gathering: order and trust. People want to know what is on the agenda, how long they will be held, and that the questions they raise reach the right people. They also want to be sure the room is only for those who were meant to be there, because a quarterly update often carries things that should not leak.
So a town hall page does two jobs at once. It publishes the running order so everyone arrives prepared, and it controls the doorway so only registered attendees can enter. Both matter, and neither is a nice-to-have.