The previous comments by FlyPNS1 are correct. Delta has had trouble competing at DFW
against American since they started the buildup after Braniff went under. I read an analysis that because American had more flights they had the pricing power in the DFW
market. Delta had to price their flights according to what American did. But, with the fares equal, American was the preferred carrier because they offered more flights than Delta with higher frequencies. As a result, Delta's load factor has always been lower than American's out of DFW
After deregulation Delta saw an opportunity at DFW
to become a big #2. In thos days hubs with multiple carriers were common. You had Delta and Eastern in Atlanta, American and Braniff in Dallas, United and Continental in Denver, United and American in Chicago, etc. Hindsight is 20/20, but it has since been proven that a hub cannot support two major airline operations. Chicago is the exception because it is such a large market and the slots have artificially maintained competition.
I would love to see Delta buy a plane like the new Embraer 170. Then it could have its 70-seaters out of DFW
but with the comfort and room of a bigger plane.