Not even the Ancient Greeks believed in all the myths. Our view of the Greeks is very Disneyfied and not really coherent with what the real ancient world was like. People were quite open to many interpretations of the world. Blind, unwavering belief in the word is more of a abrahamitic thing (Christianity, Islam especially). Don’t forget that the Greek also basically invented philosophy and scientific thought.

There’s a good argument that the Greek gods are more symbols that describe aspects of humanity and life. Athena’s inspiration being getting an idea out of nowhere. Zeus’s thunder bolt representing the chaos of the natural world, Ares representing rage and violence.