While kingdom villages are being sacked and burned down, AI will chase after bandits. Even when it has superior numbers. To be fair it had first set raiders as the target, but then changed it's mind. It happens a lot that it changes it's mind. In same game I had witnessed how was 300 army besieging castle that had just 80 garrisons. Just as it almost finished prep rations it changed mind, to go day or more away to help some other castle that was besieged. Then after few second it changed it's mind again.
Here is SS how it's chasing bandits instead of engaging raiders:
Here is SS how it's chasing bandits instead of engaging raiders: