Here's why Southwest Airlines expansion into DFW Airport is unlikely, even after surprising Houston and Chicago announcement

Dallas-based Southwest Airlines Co. (NYSE: LUV) made a big splash Oct. 12 when it announced intentions to fly out of George Bush Intercontinental in Houston and O'Hare International in Chicago. In both Houston and Chicago, Southwest has historically stayed out of the bigger airports, George Bush and O'Hare, and instead dominated the traffic at the cities' smaller, secondary airports: William P. Hobby in Houston and Midway International in Chicago. Notably, Southwest uses the same strategy in North…