Lack of supplies: The Crusades were often poorly supplied, and the Crusaders often had to contend with shortages of food and water. This made it difficult to sustain a siege for an extended period of time.
Disease: Disease was a major problem for the Crusaders, and many soldiers died from illnesses such as dysentery and typhus. This further weakened their ability to conduct sieges.
Guerrilla warfare: The Crusaders often faced resistance from the local population, who would use guerrilla tactics to harass the Crusaders and disrupt their supply lines. This made it difficult for the Crusaders to maintain a siege and capture a city.
Muslim resistance: The Muslims were often well-organized and determined to resist the Crusaders. They often used a variety of tactics to defend their cities, including sallying out to attack the Crusaders or using siege engines to damage the Crusaders' siege works.