A spontaneous idea: Hinamizawa is viewed as a singular, unifited entity with regards to the murders, right? I mean, that’s what the whole “You’d get away with a murder in broad daylight.” segment was about.
Assuming that the Great Hinamizawa Disaster does not occur after all arcs (I don’t think it does, given the table above- unless we consider that some mechanism behind the scenes delays the Disaster by several days), then we can reasonably assume that there’s a deliberate intent in the triggering of the Disaster.
…So perhaps the fact that the Great Hinamizawa Disaster occurred means that there’s a second “faction”, so to speak, which is fighting against the Hinamizawa entity. That likely entails stopping the curses from occurring, which is the most severe manifestation of Hinamizawa’s unity in the story. So the “perpetrator” we’re looking for, the acting force behind the curses, is the opponent of some other “faction”, which could be anything from a single person to some organization.
In Tatarigoroshi and Himatsubushi, this “second faction” wins against the perpetrators of the curse. How? I think that they fail to find the actual perpetrator. However, they likely believe in the person theory- so how do they ensure that they kill the culprit? They kill all of Hinamizawa.
For whichever reason, and assuming that the GHD always happens on the same day if it happens, the Disaster is not triggered in Onikakushi and Watanagashi.
Alternatively, I would consider Takano playing a role (i.e. she kills the whole village to evade the wrath she draws upon herself by entering the shrine storehouse), but that is disproven by the fact that the Disaster does not occur in Watanagashi and the fact that (although I believe that she altered dental records and ran away) her corpse is found in the mountains.