When he comes out from the palace right after he has blinded himself, Oedipus says:
"Darkness, dark cloud all around me, enclosing me, unspeakable darkness, irresistable--you came to me on a wind that seemed favorable."
Clearly Oedipus equates his moral darkness (his sins against mother, father, nature, and the gods) with his literal darkness (blindness). When the Chorus is amazed at the nerve it must have taken to commit such an act and asks how he could have done such a thing, he answers it was Apollo who gave him the nerve.
"But the hand that struck my eyes was mine and mine alone. What use had I for eyes? Nothing I could see would bring me joy...What was there for me to look at, to speak to, to love?"
So there you have reason number one--he had nothing to see which could bring him joy, so why look at all. The second reason follows:
"What I have done was the best thing to do.... With what eyes could I have faced my father in the house of the dead, or my poor mother?...Do you think I longed to look at my poor children, born the way they were? No, not with these eyes of mine, never!...After I had exposed my own guilt...do you think I could have looked at my fellow citizens with steady eyes?"
Reason number two, then: He could not bear to see the horror or whatever else would have been on the faces of those he once loved.
The entire concept of blindness and seeing is so symbolic in Oedipus' guilt and shame. No one really blames him for this deed--or tries to convince him he shouldn't have done it