Why were cardinals given the right to elect the pope?

Cardinals were granted the exclusive right to elect the pope primarily to protect the papacy from the influence and interference of powerful Roman families and secular rulers, such as the Holy Roman emperors.123

During the 11th century, as part of the Gregorian Reform movement, the church sought to restore its independence and distinguish the clergy from other societal orders. In 1059, Pope Nicholas II issued a decree that reorganized the cardinals into a formal advisory body and vested them with the authority to name new popes. This shift was intended to curb the long-standing practice where secular authorities or local factions controlled or imposed their own candidates on the papal throne.312

Additionally, because cardinals originated as clergy incardinated in the diocese of Rome, their role as electors maintained a connection to the ancient tradition that the bishop of Rome should be chosen by the clergy and people of the diocese. This process was later further refined and secured through the establishment of the papal conclave in 1274.21