Hello there!
Greek tragedy developed from religious festivals.
Greeks were believer people. In the place, gods and goddesses were highly worshiped and loved by people. Offertories and major tributes or presents were given to the gods in exchange of blessings for the people. However, if by any reason the gods were not pleased, they usually punish the town, the habitants, ending up in many tragedies that occurred in Greek history.
Hope this helps.