Wow. I bet some of the families that have lost loved ones that didn't have basements would tell you it's not worth it to save a few hundred or few thousand bucks.There's currently some debate going on as to the actual reason for this. Many people will say that the soil in C OK is very impermeable and clayish so that water doesn't soak into it very well and that will lead to higher maintenance costs and water leaking into the basement. While there is some truth to that, I've also heard it's just a money and effort issue. I have also been told that if you have a basement, you need to keep the soil within a foot or so of the foundation constantly moist because dry soil shrinks away from the wall and can leave the foundation unbalanced or prone to damage. People don't want to pay for the extra construction (apparently due to the soil issue, it is a bit more expensive compared to other parts of the world). Given Oklahoma isn't the wealthiest state in the country, I think many people and businesses would just rather save money. Hopefully someone more knowledgeful than me can chime in on this, though, as I'm only providing second- or thirdhand information.
I could understand if the land was rocky like in Tennessee where it's difficult almost impossible to dig a basement due to all the hard rock beneath the surface, but they don't get hit with the vast number of tornadoes that those living in Oklahoma experience.