It may be as simple as the logical consequence of manufacturing consolidation. When everyone's livelihood depends on one customer's operations, no one can dare tell that customer that this process is deficient. Anyone who does gets ostracized..
I'm totally certain that lots of people knew about the design weaknesses of the Max, just as they did about the QC failures in the 787. Some heroes tried to sound the alarm, no one wanted to hear it.
In a world where there is one US and one European jetliner manufacturer, who can dare to speak up?