Alma 52:21

And it came to pass that Moroni, having no hopes of meeting them upon fair grounds, therefore he resolved upon a plan that he might decoy the Lamanites out of their strong holds.

Moroni had no hope of meeting them on fair ground. So he came up with a plan to trick the Lamanites to come out of their strong forts.

Since Moroni had no hope of meeting them on fair ground, he came up with a plan to draw the Lamanites out of their strongholds.