The abstract noun "favor" can be stated as an action. Alternate translation: "Act kindly toward us" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
The full meaning of this statement can be made explicit. Alternate translation: "because we did not get wives for each of them during the war with Jabesh Gilead" (See: [[rc://en/ta/man/translate/figs-explicit]])
This refers to the men of Shiloh. They did not voluntarily give their daughters to the Benjamites, and therefore did not break their promise not to do that.