Let's also not ignore enterprise realities: in your example, Samsung Displays is likely giving a great price to Apple for displays based on long-term commitment of large quantities: it allows them to optimize production and possibly give a better price than maybe Samsung Mobile for smaller-runs of phones.

Each division also cross-charges, so Samsung Mobile would be paying Samsung Displays for the screens, and possibly at a small, guaranteed and non-negotiable margin.

Without a global strategy not to do so, divisions within an enterprise optimize for their own bottom line and have internal discussions on build-vs-buy even if they have an internal factory.