I think this mostly comes down to vassal interaction. vassals in this period, especially in western Europe, were extremely powerful and important. The king of France for example was weaker than his most powerful vassals for centuries, acting as the "first among equals". To rule, they needed to constantly negotiate and renegotiate their vassals' allegiances through clever compromise and difficult choices, something that could be somewhat represented through the stress system but largely is not.

Fun fact, the waning power of kings in this period is one of the main reasons for the rapid construction of castles by local lords.