One of the premises of Buffy the Vampire Slayer is that extra amounts of weird things because Sunnydale sits on a Hellmouth.
The show mentions that Cleveland also has its own Hellmouth, and an issue of Spike mentions that there is yet another on Easter Island.
Buffy's presence in Sunnydale keeps the demons and other nasties in check - but is there anything particularly special about this Hellmouth? The other Hellmouths clearly do not need a Slayer-level protector to keep the world from ending (evidenced that during seasons 1-7, Buffy only travels to Cleveland in the Wishverse). Why does Sunnydale attract the extra big/bad stuff?
I'm hoping/looking for an in-universe explanation and not something like "there wouldn't be a show otherwise".