SWA is known for keeping costs low, and part of the way that they do that is by not having backup plans at hubs, they fly point to point. So, one mistake (whatever the reason may be) causes rippling issues. If you recall about 2 or 3 years ago, all of the SWA planes were sitting on the tarmac at JIA for hours and hours because they made a staffing mistake and had no one to staff the gates. Probably a similar issue here. It's how SWA operates specifically to keep costs down, similar to how they only fly one type of jet rather than a fleet of several types.

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