Sure there is. Time. At its small airports, Southwest can have a plane touchdown, taxi, park, unload, reload, taxi, and take off quickly. Indeed, Chicago-Columbus-BWI is less than an hour longer than Chicago-BWI. Big airports wouldn't work with a business model that requires rapid flight turnaround.
I live near DFW. American Airlines has a turnaround time of 40 minutes - that's pretty fast. If Wright is repealed and American and other airlines start flying out of Love, Southwest won't be turning their flights around as quickly as they are.