"You're the Reason God Made Oklahoma" is a 1981 single from the film Any Which Way You Can, performed by David Frizzell and Shelly West. It was written by Larry Collins and Sandy Pinkard (of Pinkard & Bowden). The song was Shelly West's debut on the country chart and David Frizzell's second hit on the country chart. "You're the Reason God Made Oklahoma", was the most successful of seven country hits by the duo, staying number one on the country chart for one week and eleven weeks in the Top 40 country chart.

Based on this passage, who sings your the reason god made oklahoma? Let's give stream of consciousness first:
The relevant information to answer the above question is: "You're the Reason God Made Oklahoma" is a 1981 single from the film Any Which Way You Can, performed by David Frizzell and Shelly West.
So, the final answer is David Frizzell and Shelly West.