Untrained levies with farm tools were not really worthwhile in medieval warfare. In a straight up fight between a random guy with a wood pitchfork and a trained soldier with a spear, short sword, shield, chainmail shirt and helmet nine times out of ten the soldier will beat the rando. If there are ten or more of these guys they can form a shield wall and the odds lean even more in their favor. In practice things are even more one sided because the untrained mob knows how much they suck compared to the actually competant well equiped guys so some of them would soon run, which would lead to the hold mob routing.
An Army marches on it’s stomach. A human needs to eat about 1-2 kg of food a day, supplies that they A: have to carry on their person (maybe 40kg tops), B: rely on pack animals or animal drawn carts for transport which need their own food (two oxen could pull about 1,500kg and each beast and would consume 20kg a day) or C: forage the countryside (which also means stealing from local peasants) for food. In the middle ages logistics was handled ad-hoc without a professional quartermaster’s corps. Unless you are on the defensive you don’t want a massive mob of thousands of untrained peasants who’d route at the first sign of trouble in medieval warfare, better to have a mobile force of a few hundred knights on horseback in (depending on era) maile or plate that have been trained from childhood supported by a thousand Men-At-Arms, common born infantry retained by the local lords with some serviceable armor, arms and training.