The current war enthusiasm system can create some very strange scenarios, especially in England/France for the HYW (1.10 beta)

War enthusiasm is mostly from "balance of military" - You could have the primary nation in a war have 0 troops, the war goal occupied, and half of their country being occupied and they will still have 70+ enthusiasm because some landlocked vassal in France has 8k levies. These levies have never fought in a battle, they don't even have access to the sea to hire merc transports, but since they exist on paper it gives England the spirit to fight on.

It makes playing as Irish minors or Scotland impossible in 1.10, because even if you have 40+ WS England won't part with a single ounce of soil, since even though they have no military and most of their country is under occupation, there are 16k troops in France, which is 3-4 times the strength of the enemy. Does it matter that these troops have no way to join in on the battle? No.

IMO, if an ally or vassal has not joined the war in 2-3 years, they should white peace out, the same as if the war goal has not been contested forces you to sign a white peace.