Apple prefers to outsource the difficult, high capex, low-margin and worker rights/fair compensation encumbered aspect of their products to third parties.
Buying a manufacturer would bring all of that in-house.
That is so true. Ethics are mere marketing talk when investor profits are on the line. And Foxconn is universally considered as the "evil guy" when they are just doing exactly what Apple wants them to do: manufacture the parts very cheap. I can't recall do they also assemble them too.
Buying a manufacturer would bring all of that in-house.