Regarding costs of switching to different aircraft model - the type ratings themselves might not be that expensive, similarly parts and other preparations when

Regarding costs of switching to different aircraft model - the type ratings themselves might not be that expensive, similarly parts and other preparations when looked in isolation. Which is fine for privately-owned company, but not for publicly traded company that is going to take a pounding for the expenses over multiple quarters. And similarly Boeing wanted to have a happy path over designing and certifying a completely new plane, which is frankly what they should have done - the 737 design could not be enhanced further without at least major recertification part (for example, going full fly by wire).