Southwest Airlines grew out of Air Southwest, an intrastate carrier that Herb Kelleher started to provide air service solely within Texas. (Why? To avoid FAA regulations.) They traditionally fly into smaller airports because it avoids higher fees and because the traffic level is lower so there is less time spent on the ground. Recently, Southwest merged with AirTran Airways. For what it's worth, the limericks and gags came from Southwest, not ATA. It's part of their culture.
Southwest does fly into Dallas, but they do so into Love Field (DAL). That's where their ticker symbol comes from; Dallas Love Field was their primary airport for years and still serves as the airport where they have almost complete control and their corporate HQ. They still fly from Love because DFW is almost completely controlled by American Airlines. Southwest was even the direct target of a law (the Wright Amendment) that artificially hobbled service at DAL--and the law only recently started to phase out of existence--because Braniff-now-American didn't want the competition. Neither did Fort Worth, because Dallas and Fort Worth went in together on the construction costs of Love and both were supposed to close their city-owned regional airports to commercial traffic. Fort Worth closed Meacham Field, Dallas didn't close Love Field. Fort Worth sued and lost, so Fort Worth-based Braniff, followed by Fort Worth-based American, lobbied for the law.
Southwest does fly into Dallas, but they do so into Love Field (DAL). That's where their ticker symbol comes from; Dallas Love Field was their primary airport for years and still serves as the airport where they have almost complete control and their corporate HQ. They still fly from Love because DFW is almost completely controlled by American Airlines. Southwest was even the direct target of a law (the Wright Amendment) that artificially hobbled service at DAL--and the law only recently started to phase out of existence--because Braniff-now-American didn't want the competition. Neither did Fort Worth, because Dallas and Fort Worth went in together on the construction costs of Love and both were supposed to close their city-owned regional airports to commercial traffic. Fort Worth closed Meacham Field, Dallas didn't close Love Field. Fort Worth sued and lost, so Fort Worth-based Braniff, followed by Fort Worth-based American, lobbied for the law.