Why was hades sent to hell?

Hades was not sent to hell; rather, he is the god of the underworld in Greek mythology. After the defeat of the Titans, Zeus, Poseidon, and Hades divided the cosmos, with Hades receiving dominion over the underworld. His role was to oversee the dead and ensure that the souls of the deceased were properly judged and assigned to their respective afterlife realms. Thus, Hades is a figure of authority in the underworld rather than a prisoner or a being banished to hell.