Furthermore, while those core competencies might sound correct to Boeing, they wouldn't sound like it to Boeing's customers. You're paying Boeing for a plane and support, not a trading company that can find five other companies who can outsource each task to a different firm that delegates responsibility to...
The problem is that there's a mismatch between the customers and management as to what the core focus of the business actually is. Every business wants to become a weirdly shaped futures trader that just arbitrages on other people's work - i.e. one that has no core competency whatsoever. Everything gets outsourced so that cost pressure can be used to obfuscate fraud.
If you can get 70 airframes for five years in a way that means that you just have to borrow a nubbin of cash and then make regular payments that's what you will do. All your actual money can go to the shareholders and exec compensation. If the business (airline) folds the airframes go back to Boeing and you go on to the next gig - who cares...
If Boeing will take the risk the banks are happy to fund, local airlines - well the banks will be nervous. Every other consideration is either imposed by regulation or of no interest at all.