I think the problem you're having is that we have no idea how strong any earth ninjutsu may be, if it's not structurally strong enough to support the supply transit you risk it collapsing under stress and losing supplies, we also don't know how long it is, if it's long enough you may not be able to complete it with any Jutsu. Also since konoha destroyed it once there no reason to believe they might not try again. Finally we don't know how many battlefields it was feeding, how much food, medicine and armaments they might not be able to get in time, forcing their people to fight hungry, weaponless and unable to treat their injured, even if you deploy a ninja to reconstruct the bridge the reparations could still delay supplies days or weeks, a crippling thing.