Why did Pope Gregory VII excommunicate Henry IV for a second time in 1080?

Pope Gregory VII excommunicated Henry IV for a second time at the Lenten synod of 1080 primarily because he sought to resolve the ongoing civil war in Germany and advance the cause of church reform.12

After Henry IV had been absolved at Canossa in 1077, he successfully reasserted his authority in Germany, leading to an indecisive and protracted struggle against his rival, the anti-king Rudolf of Rheinfelden. Gregory VII, having watched this conflict for nearly three years, decided to intervene to bring about a definitive resolution. By excommunicating and deposing Henry once more, the pope formally recognized Rudolf as the legitimate king.312

This second excommunication was also tied to the broader Investiture Controversy, as Gregory had formally prohibited lay investiture at a council in 1078. However, the move was less effective than the first; it faced criticism from some nobles who felt the prohibition infringed upon their rights as patrons of churches and monasteries, and it ultimately failed to prevent Henry from securing victory in the civil war.312