Originally Posted by
Metal Gear Rex
Simple Answer: Bad AI.
Detailed Answer: The AI has a poor selection of priorities, and on top of that, once the creature gets hungry/whatever, it subtracts from their mood no matter what task they're doing. They could be trying to go to bed because they hit the max Time Awake for themselves, then become Unhappy due to a lack of Pay. The game also handles Unhappy and Angry Creatures poorly as well. An Unhappy/Angry Creature will often prioritize sulking/leaving respectively rather than making themselves happy by getting what they want, due to their Unhappy/Anger Job.
Additionally, when Unhappy/Angry, sometimes/often they will ignore the stun from a drop. This has problems on its own as the Creature AI only registers being dropped in a room once it gets up from a stun. (This also can be abused with lightning to imprison a Lord, Stone Knight, Skeleton, etc which are all normally uncapturable) As a result, if you have an Unhappy creature and if you try to drop them in a Treasury to pay them, they will still leave immediately to go sulk because they haven't been paid. You'll have to drop them multiple times to get around that.
In Short: DKII is retarded.