kingdom size, military strength, lord relations, number of factions they're at war with etc. In terms of explaining the behavioural differences you ask about (feasts, diplomacy, allocating conquests, lord relations) and others, if we assume there isn't anything about different personalities in the code then we have to assume its all circumstantial i.e. And yet people do seem to find that kings behave in the same way and lords having different personalities is well established.
I have been unable to find anything in the scripts about kings having different personalities.
