The Wizard is ...
Jealous. He doesn't hate magic, he hates he can't do it. A woman was his boss and he resented her. He goes someplace where he thinks his science would make him a god to the primitive locals and a woman uses magic to outdo him. In Oz it appears only women can be witches, so out of jealousy and spite he called himself a wizard to compensate for his lack of actual magic. Now we find out his science didn't stop the beast forever, it was apparently magic, since only magic users are trapped in the prison where the key to him controlling the giants is.
Nemo Unus Animabus Carnem!