Why did Frederick II travel to the Holy Land despite being excommunicated?

Frederick II traveled to the Holy Land despite his excommunication primarily to fulfill his long-standing Crusade vows and to assert his claims as the king of Jerusalem.12

Having married Isabella (Yolande) of Brienne, the heiress to the throne of Jerusalem, Frederick possessed a legal claim to the kingdom. Although Pope Gregory IX had excommunicated him in 1227 for repeated delays in launching his expedition—exacerbated by an outbreak of plague among his forces—Frederick chose to ignore the ban and set sail in 1228.123

His decision was driven by a broader imperial design that integrated his interests in Sicily, Italy, and the East. Once in the Holy Land, he successfully utilized diplomacy rather than military force to negotiate the return of Jerusalem, Bethlehem, and Nazareth from the Sultan al-Kāmil of Egypt. By crowning himself king in the Church of the Holy Sepulchre in 1229, he solidified his status as a sovereign ruler before returning to Europe to reconcile with the papacy.12