Government contracts.
Such as the KC-46 that the Air Force keeps refusing deliveries of because of quality issues. (The defective refueling system appears to be acceptable, however). And politically fueled purchases of outdated fighters and less than suitable anti-submarine warfare platforms.
Nothing wrong with the planes themselves, even the USAF admits that, it's that workers keep leaving garbage and their tools in the planes, often behind panels. An argument could be made that workers who are that careless may be also careless when assembling, but that doesn't translate into the plane itself being designed poorly.