I think that admins should put like, a maximum amout of mice count in a room. Because too much mice in a room causes lag, glitch and bug. And it disturbs the event maps.

There's already a maximum limit (of 25 I believe) on mice that will automatically join rooms (when they first log in or click through the room list), although if they type /room [roomName] manually they can still join.

Often when there's too many mice in one room, mods will lock the room, so players won't be able to go there anymore. This usually only happens when theres 100+ mice.

When there's 50+ mice, everyone will appear to be wearing nothing, to reduce lag.

And as Shamousey said above, there's probably a limit for the amount of mice in a room.