Two things are important here, beyond the loss of the city. The first is that the Nephites were “slaughtered with an exceedingly great slaughter.” The Nephites are already vastly outnumbered, and their physical numbers are diminishing. Their fighting population with the skills to resist are dwindling. Attrition is on the side of the invaders.
The second point is that the women and children are again sacrificed to idols. This tells us that this is a part of the cultural catalogue of these invaders. It is not something done to infuriate the enemy. The last time it occasioned a fierce response. There is no fear on the part of the Lamanite/Gadianton army that this will happen again. Again, they take women and children prisoners, and they are destined for sacrifice.