That’s not really any different from how Airbus works (and explicitly so).
But I learned that Boeing literally outsourced the fuselage and that makes you wonder if they are really fit to build airplanes…
They got something out of spawning a new corporate entity. Without a convincing TL;DR I think most of us will assume it's for reasons that sound good to Boeing business people, but not to outside people. (I. e. being a "new entity" to avoid existing labour contracts, or serving as a liability firewall in the event chunks of plane start flying off)
Their larger planes are assembled in Toulouse, but smaller planes are made globally.