The Greeks didn’t have modern science, and they didn’t have much of what we have today. So of course when the earth trembled, they figured it was a monster roaring. Or when a storm hit, that meant a god was angry. They had no way of knowing that when the earth trembled it actually meant that the tectonic plates were moving. They couldn’t have known any of this, so they made up stories to explain the world around them. But not all of the parts of these myths are even from those times. Take the Minotar for example, the Greeks actually did believe that there was a monster under earth but it was never a bull. That was made up later to add interest to the story.
There is one particular myth I find interesting-- the myth of Prometheus. The myth says that Prometheus the titan (not god) gave the humans fire. It says that Zeus wasn’t sympathetic towards the mortals. The Greeks said that when Kronos and his army of titans defeated the gods, the titans were thrown into Tartarus. Obviously Prometheus wasn’t thrown out, and Zeus kept him to create humans. But when Prometheus gave fire to the humans (the one thing he wasn’t supposed to do) Zeus got super angry and chained him to a huge boulder and cursed him so an eagle would come to him every day and eat his liver. So I think the Greeks had to give the gods a stubborn side as well as a divine side. They must have believed that if the gods had a good side they must have a bad one too.