If the community is so large that your post is immediately buried, it’s large enough for a subcommunity.
However, most communities on the threadiverse are not that large. In that case, fragmenting the tiny communities even more just hides your post from the users who might be interested but are not subscribed to a niche subcommunity of a small community.
Cities which had someone blow a horn to wake everyone up would also have watchmen walking the city at night. Presumably, they would wake the next person up when their shift ended so that someone is awake at all times.