Medieval arrows were expensive things. Each arrow cost about the same as a day’s wages for the average man
Unsurprisingly, archers did not want to waste arrows, and so shot only when certain of a target. When going on campaign a man was expected to supply all his own clothing and equipment, which usually included 24 arrows.
However, the revolutionary ‘arrowstorm’ tactic adopted by English armies in the Hundred Years War demanded vast numbers of arrows. Each archer was expected to shoot six arrows in just 30 seconds at an enemy formation. In the course of a battle each man might use up to 100 arrows.
The cost of such quantities was beyond the pockets of archers, so if the king wanted them to use such numbers of arrows he had to pay for them himself.
For the Agincourt campaign, King Henry V bought 300,000 arrows, along with dozens of carts to move them across France.