Because of regulations, because of contracts, because of a myriad reasons I won't waste my time listing here.
The point is that they have been in business for over a century, that the aerospace industry is heavily regulated, and so I somewhat expect them to have processes in place and responsibilities to make sure the planes are delivered and remain according to their design specification.
And you don't strike me as someone who knows more than me (a total newbie) on the matter, so maybe we stop wasting each other's time on a pointless argument about shit that is absolutely beyond us both. Yeah?