The article indicates "upwards of 50% of our aircraft lines flow through Florida".

There's more to Florida than just Miami, and the FAA backs up the weather claim.

Meanwhile, none of the other airlines who also instituted mandates saw delays.

"This appears not to be an aviation problem so much as a Southwest problem; other airlines were able to carry on with minimal cancellations after Friday’s disruptions."

"Southwest has generally struggled with coordinating its operations as of late; it had the highest percentage of cancellations and worst on-time performance among the country’s four major airlines in June and July. The Southwest pilots union further blamed the company’s technical systems and processes for reassigning pilots when disruptions occur, claiming that these are long-standing problems that executives have failed to fix for years. The airline has struggled with rerouting pilots partly because it uses a “point-to-point” system, which focuses on flying passengers directly to their destinations. This is opposed to the “hub-and-spoke” model that American Airlines uses, in which passengers are often first routed to a main base of operations before departing for their final destination. While the point-to-point system has the advantage of reducing travel times and the number of connecting flights, it can be difficult to adapt to unexpected situations. Southwest’s point-to-point network also covers an unusually large geographic area, which makes reassigning pilots even more complicated."