"The Tulsa World got ahold of the memo ..."
That's why. The lib paper in the state, which has nothing to lose because it's in Tulsa, not OKC - the actual bombing site with its name attached forever in infamy - doesn't mind expending its energies trying to track down anything that might lead back to a Pubbie somewhere being at fault, as in Bush41.
The O'homan OTOH, bless their hearts, won't expend any energy at all doing anything. They just don't. Ever. Some of the letters to Dear Abby make them cringe; they're that "conservative" in the "to the right of Attila the Hun" sense.
So am I, but my mind's a little more open. Maybe with a sho-nuff oil boom back on, they'll kick up their heels a bit, as in the old days, and go back to snooping around. But don't count on it. As long as the Baptists and Muslims peacefully co-exist in the community, which they have for a long time - and I won't say out loud why that is - everyone can eat falafel and hummus and no one's sensibilities are upset.
While I understand the root of your position (Tulsa World = lib, DOK = extreme conservative), this seems more accurate historically than it is currently. I have noted considerable liberalizing since Christy took over after the passing of her father, including on the editorial page.
I think the reason they don't pursue this is journalistic laziness and conservatism in the sense of seeking to maintain the status quo. In addition, they don't want to be seen as the latest iteration of the "grassy knoll" group, at least in their own mind.