To be precise, most had "died" in the proposal stage.
Calling it a "safe zone alliance" was misleading.
In reality, forming such an alliance was akin to creating a larger safe zone.
The leader of the central safe zone would not only retain their position but even increase their authority, while the leaders of the other zones would essentially be placing themselves under a superior.
Anyone with a bit of self-interest wouldn't be so willing to give up their own power.
Unless the central safe zone was so overwhelmingly superior that no one else even considered opposing it.
And Pyeongseong Safe Zone was exactly that.
The proposal to form an alliance didn't come from Pyeongseong Safe Zone but was instead suggested by the surrounding safe zones.
Rumor had it that they had privately considered it after the Spring Trade Fair, and the Haneulsae Safe Zone incident had solidified their decision.