Why did the Greeks worship Zeus, Hades and Poseidon?

Because these were the most important gods in ancient Greece. They were siblings. Zeus was considered the most supreme god – the main Olympian, who ruled the world from the top of Olympus itself. At the same time, Poseidon, at that distant and legendary time, was the ruler of the seas. Hades ruled the kingdom of fear and darkness – the world of the dead, where the souls of the dead fell. Thus, in those ancient times, the world order was established. Almost everything depended on the will of these three gods.