Because Boeing is 'too big to fail', proven in the last 737 Max case with MCAS. If there were no leadership prosecuted for that travesty and tragedy, none will ever be for this one. Proper accountability would cripple both the civilian and military sides of the US aerospace sector, which is dominated by Boeing.

So Southwest is all-in on not just Boeing, but 737s. That's their entire fleet. It makes a lot of things simpler. Could they boycott and switch to Airbus? Possibly, but at massive cost and logistics nightmares. Given their logistics failures elsewhere, they'd be fools to try to exit Boeing over this.