Since Benjamin has yet to repent, this compassion is falsely based. Israel apparently wants to desperately maintain a formal order among the twelve tribes. That is, they were less concerned with living as a holy nation, fleeing from the Baals and Asherahs, than having all twelve tribes accounted for and formally having peace—while there was no true peace with the Lord! Israel is valuing a false sense of kinship over the will of the Lord.
15 And the people had compassion on Benjamin because the LORD had made a breach in the tribes of Israel.