It's not only the dice games that are illegal in Oklahoma but also the wheel games and I'm not too sure why they passed that law that banned them. I hope someone here from there can elaborate on the matter.
I have no idea why they passed that law but Oklahoma like a few other places seems to have banned games of chance, claiming they are gambling. They've also banned casinos and casino dealers (Oklahoma Gambling Laws.) Games of skill are considered gaming and exempt from the ban.
The thing about the US is that the states are autonomous and so much as gambling is legal is one state, it can be banned in another. You guys may want to look at the Oklahoma gambling laws posted by @AlltheAces. If I may ask, what are these games of skill?
If I remember correctly it is a way of saying that the legislature realised they couldn't ban decks of cards.
This distinction is why many of these phone-in competitions have an easy-to-answer question to get entry to a draw. You know the type: "Is the White House a) The home of the President or b) a cabbage". They just need to be able to say winning takes an act of skill instead of pure chance.