But the thing is that airliners have the right (and expectation) to repair their own planes, with Boeing and Airbus running a very extensive repair/service arm

But the thing is that airliners have the right (and expectation) to repair their own planes, with Boeing and Airbus running a very extensive repair/service arm of their businesses. Upkeep of certain parts of the plane (engines, computers, cabin interior features) are actually also the responsibility of the sub-vendor who makes it. There also exists an extensive ecosystem of after-market repair shops and a vested interest by regulators to keep all ships airworthy to put a check on Boeing deciding to make access to a critical software update contingent on any kind of pressure sales tactic via user agreements.