Why does Zeus leave Olympus and help the Trojans?

Zeus leaves Olympus to help the Trojans primarily due to a promise he made to Thetis, the mother of Achilles, who requested that he favor her son and the Trojans in their conflict against the Greeks. Additionally, Zeus is motivated by a desire to maintain balance among the gods, as he often seeks to manage their conflicting interests and interventions in mortal affairs. By supporting the Trojans, he aims to assert his authority and influence over the unfolding events of the Trojan War.