Its because the AI use the highest movement point avaliable from every stance, and forced march seem have incredible range, that why ai keep using it, however its also bring other problem, since AI that use forced march always ended tired in reinforcement battle or worse they cant attack what they should attack, my advice to reduce the forced march movement point below what its should be normal stance have, so the AI will always stick on normal route.However AI seems to be using Forced march very often still.. Thou they have bonus replenishment stuff so it should be fine I guess.
Great stuff however mate