Why does Oedipus become king in 'Oedipus Rex'?

Answer 1

That the Theban throne was vacant and that he won both the love of his royal predecessor's beautiful widow and the respect of his future subjects are the reasons why Oedipus becomes King of Thebes in "Oedipus Rex."

Specifically, the previous king, Laius, leaves Thebes to consult the Delphic Oracle, but never returns. Shortly after Laius' disappearance, Oedipus shows up and frees all Thebes from the bullying ways and the bottomless stomach of a monstrous Sphinx that has set up camp outside the city walls. Oedipus thereby becomes the hero of all Thebes, as well as of Theban Queen Jocasta, Laius' widow and co-ruler of Thebes with her brother, Theban King Creon.

No one has any objection to Oedipus as a conquering hero and a beloved second husband. So Oedipus becomes king even though proper procedure actually is not observed. In fact, not only the newly wed royal couple but indeed all Thebes should have looked into the who, what, where, why, and how of Laius' disappearance. Thebans instead return to life as usual.

Not once does anyone in the entire city consider that the unsolved mystery of Laius' disappearance leaves the entire city, and especially the royal family, polluted and polluting in a city increasingly polluted by this one critical non-observance of divine-ordained actions and purification rituals.