Lewisc, among the very sharpest posters on this board, is indeed correct; thanks to the idiotic-and-then-some 'Wright Amendment' rule, Southwest is only allowed to fly nonstop to only a handful of cities from Love Field, a despicable rule implemented to 'protect' American Airlines in 1979.
Consequently, residents of 'Big D' pay some of the very highest airfares of any major airport in the USA; this restriction only applies to Southwest out of Love Field, since they can fly nonstops to anywhere they choose from their four other major Texas cities---Austin, San Antonio, Houston Hobby & El Paso.
Consequently, airfares on Southwest from those other four Texas cities tend to be substantially cheaper to anywhere Southwest flies than from either Love Field or DFW.
Suffice it to say, that also means substantially more and lengthier nonstops, as evidenced by the fact that you can fly nonstop on SWA to Nashville, Chicago, Phoenix, Los Angeles, Las Vegas, Tampa and Orlando from any of those other four cities, but not from Love Field.