When the third person died, nearly half of them started changing their minds, hoping to negotiate with Li Ang and seek a non-violent solution to the issue.
When the fourth person died, the advocates for negotiations had gained an overwhelming advantage, canceling military operations and promising Li Ang all sorts of things. Indeed, letting bygones be bygones was not enough; they even had to compensate Li Ang for the psychological harm he had suffered.
At this level of carnage, it had about reached its limit. It was impossible to kill them all. While powerful himself, he had none of the cultivator's abilities to behead someone from miles away; killing one person required traveling to a location, making the efficiency extremely low.