Hes the top heel in the company and the best thing they got going right now honestly so it just makes sense for him to hold the strap. Its a lot of people who tune into smackdown just to see what he gonna be on, so why would you not want your main title on that guy?
Owens was a great opponent but what could they have done with him if they gave him the title and took Reigns out of the picture? chances are they would of put him in a feud w/ somebody like Baron Corbin or they would of just reignited the one that he had Rollins over on RAW.