Because of the unexpected incident involving Hanyang's mother, Li Dai's trip to save people took nearly a year and a half. Originally, saving people wouldn't have taken that long, but on her way back, Li Dai simply could not stomach the Insect Sect's cruel methods against mere toddlers, so she intervened.
When she encountered children in trouble, she saved them. This followed her core nature without a moment of hesitation. As for why she didn't simply wipe out the Insect Sect root and branch—well, after she left, more children might suffer in the future, but that was no longer her concern. She only saved those she happened to pass by and encounter; she never actively sought out trouble to play the hero. Those she ran into were a matter of fate; for the children she never met, that was simply their lot.
In any world, people suffer tribulations every single moment. If one truly tried to save everyone, it would be an impossible task.
Chapter 977