I would think part of this has to do with changed recruiting practices brought about by the French levee en masse (mass draft) during the revolution. Compare to the generation before, when wars were fought largely with mercenaries, as a gentleman's game. If your foreign mercenaries die, you can hire new ones and start again. As long as you haven't suffered an invasion to your territory, and as long as taxes haven't gone up too high, your populace might by-and-large not even notice that they are at war.

But when every third or second son is fighting abroad, the economy doesn't function, families are wrenched apart. There is a short-term advantage: the populace becomes invested in the war. But you better win fast, or at least win, or you may well face a revolution at home. The best demonstration of this dynamic is World War One, when basically all of the losing countries underwent some kind of revolution.

Worth pointing out too that in some feudal societies, the armies were based on a local levy. I'm thinking of the English fyrd during the Norman invasion. Kings then faced a similar problem - they needed to execute wars quickly and victoriously or risk damaging their economies or losing power to local aristocrats.