Spirit also contracts with Airbus. Did Boeing just get unlucky?
Airbus apparently takes way more "partnership" approach to contractors.
The thing is, we have regulations on how one has to run aircraft manufacturing, maintenance, repair, and operations, BECAUSE of all of that.
Complying with them is considered cost of doing business. If you can't, it means you're no longer fit for the market.
And Boeing pretty clearly let the quality assurance required of them fail.