It's easy to recover the bombs after completing a round of shooting during training, but in reality, there's seldom an opportunity to recover them on the battlefield. Only after the fight, and only if victorious, do you have the right to clean the battlefield.
If you lose or make a tactical retreat, it's equivalent to abandoning that part of the ammunition. In this era, the production of metal is still very low, otherwise Lance wouldn't need to import iron ingots from Totnes.
It can be said that every shot fired with iron shot and gunpowder is not just bombs flying out, it's money flying out!
Not to mention, the cost of iron shot is expensive, and the craftsmanship is troublesome. Therefore, it's difficult to replenish the consumed projectiles after such a battle, putting enormous pressure on logistics.
Moreover, if you encounter a siege warfare, when facing enemy fortifications, using iron shot could potentially allow enemies to reuse them.
