Any siege involved more than cannons, shovels, night attacks... Additional factors complicated matters.
As discussed earlier, the first step in the siege was for the attackers to invest the artillery fort and its environs. By surrounding the defenders as quickly and thoroughly as possible, attackers could deny defenders any reinforcements, weapons and munitions from being rushed in. For the attacker, success of a siege rested with ensuring the besieged were sealed inside with no means of supply. Their resources went down day by day, week by week, like the sand in an hourglass.
As important as reinforcements and munitions was food. All defenders required food every day. Starvation was a weapon. A saying goes: "A hungry man is a dangerous man but a starving man poses no danger." In order to succeed, the attacker had to nullify as much danger as possible. What artillery and musket fire did not do, denying food would. In addition, starving men became susceptible to disease.
Even if a defending soldier was not dead or prostrate from starvation, his fighting abilities were certainly diminished. His aim may have gotten wobbly and his rate of reloading slowed. If the fight came to hand-to-hand combat, his reflexes and endurance were not what they had been. He had become a half soldier.
The strongest walls and finest engineering did not stave off starvation and its cohort, disease.