Google is also a trillion dollar company, as other have pointed out Soutwest is a low-cost carrier which most probably doesn't have the luxury of hiring FAANG-level engineers on 500k yearly comp in order to best simulate "black swan" events.
Source: Am a local who's been headhunted by them a few times but never got beyond the initial discussion with the headhunter for this reason.
If you have a black swan event like this and you listened to your solutions architect you will have a disaster recovery plan or even better a multi region setup. Worst case you have highly paid support engineers at the cloud providers who will do everything they can to get you back online.
That's not the article I hoped to find however. I seem to remember there was another article where they hired a investigator/consultant to figure out the price to migrate to the cloud and ensure "this never happens again."
My recollection of that was: their scheduling/ops team is also in the same city (Atlanta GA) as this datacenter, and that teams work was brought to a halt by the datacenter outage. The investigator concluded that Delta would need redundant copies of the ops team or the whole effort of moving the software to the cloud would just be at risk to something happening to the human team all in the same city. That would obviously cost to much money, so Delta decided to skip it.
Amadeus are eating them up, because their airline backend system is a shared multi-tenant setup, built on commodity hardware. Their distribution system used to be mainframes, but they managed to migrate away in the 2010s.
Sabre is still alive, but only in North America, and Amadeus is slowly chipping away (WN, AC..)