The Nephites desired to recover all of their lost territory, and Manti was a particularly important fortified site, for it controlled one the major passes that allowed travel between Lamanite lands in the south and the Nephite lands north of the strip of wilderness. Unfortunately, they were unable to fulfill their desire. The Lamanites had greater numbers, and Manti was a fortified location.
The Lamanites were quick to learn that a feint might attempt them to split up their forces and might lead to a defeat. They refused to fall for it. A historical question to be asked is how they learned of the previous attempt, and the answer is that it would be highly unusual for every single Lamanite to have been killed. Some must have escaped, or perhaps even deserted. That allowed someone with the understanding of what had happened to make their way back to the Lamanite lines and let them know that they should beware of that particular ruse.